Flat non-aqueous electrolyte secondary cell

ABSTRACT

In a flat non-aqueous electrolyte secondary cell comprising an electricity-generating element including at least a cathode, a separator and an anode and a non-aqueous electrolyte in the inside of a cathode case, a plurality of electrode units each consisting of the cathode and the anode opposite to each another via the separator are laminated to form an electrode group, or an electrode unit in a sheet form consisting of the cathode and the anode opposite to each another via the separator is wound to form an electrode group, or a sheet-shape cathode is wrapped with the separator except for a part contacting at inner face of cathode case and a sheet-shaped anode is set on the sheet-shaped cathode in a right angled position each other and then these cathode and anode are bent alternately to form an electrode group, and the total sum of the areas of the opposing cathode and anode in this electrode group is larger than the area of the opening of an insulating gasket in a sealed portion in the cathode case or than the area of an opening in a sealed plate in a sealed portion in the cathode case, whereby the discharge capacity upon heavy-loading discharge is significantly increased as compared with the conventional cells. Accordingly, while the size of the cell is small, the discharge capacity is increased as described above, and thus it is possible to provide a highly utilizable flat non-aqueous electrolyte secondary cell. Further, in said flat non-aqueous electrolyte secondary cell, problems which may be caused by the increased discharge capacity in the cell can be solved by improving the solvent and supporting electrolyte for the electrolyte or by various improvements in the cathode and anode cases.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a flat non-aqueous electrolytesecondary cell and in particular to a flat non-aqueous electrolytesecondary cell with improvements in heavy loading dischargecharacteristics.

[0003] 2. Description of the Prior Art

[0004] In recent years, there are commercially available coin- orbutton-shaped flat non-aqueous electrolyte secondary cells wherein metaloxides such as MnO₂ and V₂O₅, inorganic compounds such as fluorinatedgraphite, or organic compounds such as polyanline and polyacenestructural compounds are used as the cathode active material, whilemetal lithium or lithium alloys, organic compounds such as polyacenestructural compounds, carbon materials capable of occluding andreleasing lithium, or oxides such as lithium titanate orlithium-containing silicon oxides are used in the anode, and non-aqueouselectrolytes containing a supporting electrolyte such as LiClO₄, LiPF₆,LiBF₄, LiCF₃SO₃, LiN(CF₂SO₂)₂ and LiN(C₂F₅SO₂)₂ dissolved in anon-aqueous solvent such as propylene carbonate, ethylene carbonate,butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethylcarbonate, dimethoxyethane and γ-butyl lactone are used as theelectrolyte. These cells are used as power sources for backing up SRAMand RTC where an electric current is discharged for light loading ofabout several to dozens μA, or as main power sources for wristwatchesnot requiring cell exchange.

[0005] In general, these coin- or button-shaped flat non-aqueouselectrolyte secondary cells have the structure shown in FIG. 4. That is,a metallic anode case 5 also serving as an anode terminal and a metalliccathode case 1 also serving as a cathode terminal are fit to each othervia an insulating gasket 6, and further the cathode case 1 has a sealedopening structure caulked by caulking, and in the inside of thisstructure, tablet-shaped cathode 12 and anode 14 having a smallerdiameter than the opening of the insulating gasket 6 are set up againsteach other via a single- or multi-ply separator 13 impregnated with anon-aqueous electrolyte.

[0006] The coin- or button-shaped flat non-aqueous electrolyte secondarycells as described above have the advantage that they are easilyproducible, excellent in mass-productivity, and superior in long-termreliability and safety. Further, by virtue of their simple structure,the most distinctive feature of these cells is that theirminiaturization is feasible.

[0007] Meanwhile, the miniaturization of devices (mainly compactinformation terminals) such as portable telephones and PDA is promoted,thus making it essential to miniaturize secondary cells as their mainpower sources. In these power sources, there have been used cylindricalor rectangular alkali secondary cells such as lithium ion secondarycells wherein lithium-containing oxides such as lithium cobaltate isused as the cathode active material while a carbon material is used inthe anode, or nickel hydride secondary cells wherein nickel oxyhydroxideis used as the cathode active material and a hydrogen-occluding alloy isused as the anode active material. These cells have been constructed bycoating or filling a current-collecting body consisting of a metal foilor metal net with an active material layer to form an electrode, thenwelding a tab terminal into the center of the electrode, and winding orlaminating it to form an electrode group, complicatedly bending the tabterminal from the center of the electrode group and welding the terminalinto a safety element, an opening-sealed pin or a cell can. However,these cells have been constructed in such a complicated process thatthey are inferior in workability and the miniaturization of partstherein is also difficult. Further, these cells should be providedtherein with a space for preventing the tab terminal fromshort-circuiting or for integrating a large number of parts such assafety element into the cells, and thus there is a limit to theminiaturization of these cells at present.

[0008] For miniaturization of the cells under these circumstances, thepresent inventors have attempted not at miniaturizing cylindrical orrectangular lithium ion secondary cells or nickel hydride secondarycells, but at achieving a higher output of the flat non-aqueouselectrolyte secondary cells described above. That is, the presentinventors have used lithium cobaltate of high capacity and highpotential as the cathode active material and a graphitized carbonmaterial of high capacity excellent in voltage evenness as the anodeactive material, and according to the process and structure of theconventional flat non-aqueous electrolyte secondary cell, the inventorshave processed the cathode and anode into tablets smaller than a gasket,to prepare a cell.

[0009] However, this cell though attaining superior characteristics tothe conventional flat non-aqueous electrolyte secondary cell is notsatisfactory when discharged in a large current required of a main powersource in compact portable devices, thus failing to achieve levelssatisfactory as a main power source in compact portable devices.Accordingly, the development of techniques for permitting theheavy-loading discharge characteristics of the compact flat non-aqueoussecondary cell to reach levels not achieved in the prior art isnecessary.

SUMMARY OF THE INVENTION

[0010] This invention was made in view of the circumstances describedabove, and the object of this invention is to provide a flat non-aqueouselectrolyte secondary cell, which is remarkably superior inheavy-loading discharge characteristics.

[0011] The present inventors made extensive study on the improvement ofthe heavy-loading discharge characteristics of the flat non-aqueouselectrolyte secondary cell described above. As a result, they found thatthe heavy-loading discharge characteristics are significantly improvedby allowing the area of the electrodes to be significantly larger thanin the conventional flat non-aqueous electrolyte secondary cell, toarrive at the present invention.

[0012] That is, the present invention relates to a flat non-aqueouselectrolyte secondary cell comprising a metallic anode case also servingas an anode terminal and a metallic cathode case also serving as acathode terminal fit to each other via an insulating gasket, the anodeor cathode case having an opening-sealed structure caulked by caulkingand having in the inside thereof an electricity-generating elementincluding at least a cathode, a separator and an anode and a non-aqueouselectrolyte, wherein a plurality of electrode units each consisting ofthe cathode and the anode opposite to each another via the separator arelaminated to form an electrode group, or a sheet-shaped electrode unitconsisting of the cathode and the anode opposite to each another via theseparator is wound to form an electrode group, or a sheet-shape cathodeis wrapped with the separator except for a part contacting at inner faceof cathode case and a sheet-shaped anode is set on the sheet-shapedcathode in a right angled position each other and then these cathode andanode are bent alternately to form an electrode group, and the total sumof the areas of the opposing cathode and anode in this electrode groupis larger than-the area of the opening of said insulating gasket.

[0013] Further, the present invention relates to a flat non-aqueouselectrolyte secondary cell comprising a metallic cell case also servingas an electrode terminal, an opening-sealing plate for sealing anopening in said cell case, and another electrode terminal arranged viaan insulator in an opening provided in a part of the opening-sealingplate, said cell case being provided inside with anelectricity-generating element including at least a cathode, a separatorand an anode and a non-aqueous electrolyte, wherein an electrode groupconsisting of an electrode unit having the cathode and the anodeopposite to each another via the separator is formed, and the total sumof the areas of the opposing cathode and anode in this electrode groupis larger than the area of the opening of said opening-sealing plate.

[0014] As the forms where the total sum of the areas of the opposingcathode and anode in the electrode group is larger than the area of theopening of the insulating gasket in the present invention as describedabove, there is the form (1) wherein a plurality of the above-describedelectrode units are laminated to form an electrode group, and the totalsum of the areas of the opposing cathodes and anodes in this electrodegroup is larger than the area of the opening of the insulating gasket,or the form (2) wherein the above electrode units are in the form of asheet, and said sheet-formed electrode units are wound to form anelectrode group, and the total sum of the areas of the opposing cathodesand anodes in this electrode group is larger than the area of theopening of the insulating gasket, or the form (3) wherein a sheet-shapecathode is wrapped with the separator except for a part contacting atinner face of cathode case and a sheet-shaped anode is set on thesheet-shaped cathode in a right angled position each other and thenthese cathode and anode are bent alternately to form an electrode group,and the total sum of the areas of the opposing cathodes and anodes inthis electrode group is larger than the area of the opening of theinsulating gasket.

[0015] As described above, the total sum of the areas of the opposingcathodes and anodes in the electrode group is made larger than the areaof the opening of the insulating gasket or the opening-sealed plate,whereby the heavy-loading discharge characteristics of the flatnon-aqueous electrolyte secondary cell can be significantly improved.

DETAILED DESCRIPTION OF THE INVENTION

[0016] To improve the heavy-loading discharge characteristics, it isconsidered effective to increase the area of the electrodes. In theconventional flat non-aqueous electrolyte secondary cell, however, acathode and an anode, both in a tablet form, are accommodatedrespectively to contact with an insulating gasket in the cell, so thatthe area of the cathode and anode opposing to each other via a separatorwill inevitably be smaller than the area of the opening of theinsulating gasket. Even if the area of the opposing electrodes can beenlarged to some degrees by thinning the gasket, the opposing electrodeshaving a larger area than the area of the opening of the gasket cantheoretically not be accommodated in the cell.

[0017] Accordingly, the present inventors have solved this problem froma different viewpoint from the prior art by laminating electrode unitseach consisting of a cathode, an anode and a separator, or by winding anelectrode unit, or by bending alternately the sheet-shaped cathode andthe sheet-shaped anode settled in a right angled position each other, ina cell case for the very small coin- or button-shaped flat cell, topermit the total sum of the areas of the opposing cathode(s) andanode(s) in the electrode group to be larger than the area of theopening of the insulating gasket.

[0018] In the conventional cylindrical or rectangular large secondarycells described above, there are cases where dozens electrode layers areaccommodated in one cell, but such cells have the complicated structureas described above, so it is difficult to apply the electrode structureof such cells to the coin- or button-shaped, compact flat non-aqueouselectrolyte secondary cell. Even if such a structure can be successfullyapplied, the advantages of the flat non-aqueous electrolyte secondarycell, for example miniaturizablility and high productivity, cannot bemaintained. Accordingly, there has been no study attempting atpermitting an electrode group whose opposing cathode and anode have alarger area than the area of the opening of an insulating gasket to beaccommodated in the coin- or button-shaped, compact flat non-aqueouselectrolyte secondary cell.

[0019] In the coin- or button-shaped, compact flat non-aqueouselectrolyte secondary cell in the present invention, the electrode groupis constituted as shown above in (1), (2) and (3) thereby maximizing thearea of the electrodes and minimizing the number of parts, thussucceeding in accommodating the electrode group and an amount of thenon-aqueous electrolyte necessary for discharge in the space of thecompact cell. Further, the electrodes can be easily produced accordingto this accommodation method and thus are suitable for mass-productionby virtue of superiority in productivity and production costs.

[0020] When the electrode units are laminated to form the electrodegroup in the present invention, the number of faces where a cathode isopposite an anode in the electrode unit is preferably at least 3.Cathode and anode plates, each provided with an electrically connectingportion at a part (terminal) thereof, are arranged as the electrodessuch that they are opposite to each another via a separator, wherein theelectrically connecting portion of each cathode plate is exposed in onedirection of the separator, while the electrically connecting portion ofeach anode plate is exposed in the opposite direction of the separator,and thereafter the electrodes are laminated such that the electricallyconnecting portions of the cathodes are exposed to and electricallyconnected at the same side, while the electrically connecting portionsof the anodes are exposed to and electrically connected at the oppositeside. By arranging the electrically connecting portions of the cathodesopposite the electrically connecting portions of the anodes, internalshort-circuiting upon contact between the cathode and anode electricallyconnecting portions can be prevented even in the coin- or button-shaped,compact flat non-aqueous electrolyte secondary cell.

[0021] Now, the method of connecting the electrode group to a metal caseis described.

[0022] In the cylindrical or rectangular, relatively large lithium ionsecondary cell as described above, a tab terminal is welded for currentcollection into the center of the electrode group or into a core of thewound electrode group, then bend and welded into a safety element or anopening-sealed pin. However, the technique of bending processing iscomplicated and thus inferior in productivity, and further the cellshould be provided therein with a space for preventing internalshort-circuiting, or an insulating plate should be inserted between theelectrode group and the tab terminal. Furthermore, if stress is appliedto the part where the tab terminal was welded into the electrode, theseparator may be broken and the electrode may be deformed, thus makingit necessary to protect the tab terminal by an insulating tape or toprovide the wound core with a space. Accordingly, the method of currentcollection for the cylindrical or rectangular lithium ion secondarycells cannot be applied to the coin-shaped or button-shaped, flatnon-aqueous electrolyte secondary cells having a small internal volume.

[0023] Accordingly, the present inventors have secured currentcollection for the electrode group and the cell case by exposing anelectrically conductive constituent material of the cathode at one edgeface of the laminated electrode group (face parallel to the flat planeof the flat cell) while exposing an electrically conductive constituentmaterial of the anode at the other edge face and then bringing therespective exposed electrode constituent materials into contact with thecathode and anode cell cases, respectively. According to this method,the discharge capacity can be increased without providing any space orinsulating plate between the electrode group and the cell case. Inaddition, because no short-circuiting occurs between the cell case orthe electrode and the tab terminal, the cell is superior in safety andreliability.

[0024] Further, the area of contact between the electrode constitutionalmaterial and the cell case can be made significantly larger than thearea of contact between the conventional tab terminal and the cell case,to achieve stable current collection, and the conventionally inevitableoperation of welding the tab terminal into the electrode case can beomitted.

[0025] As a matter of course, the good electrical contact between theelectrode constitutional material and the cell case, achieved in themethod of collecting current in the present invention, can be furtherimproved by welding the electrode constitutional material into the cellcase or by fixing these members via a conductive adhesive or via acurrent collecting net between the electrode constitutional material andthe cell case.

[0026] When the electrode unit is wound to form the electrode group inthe present invention, the face where the cathode is opposite the anodein the electrode unit may be in either the parallel or perpendiculardirection to the flat plane of the flat cell, preferably the paralleldirection. This is because the structure for securing current collectionis made by exposing a conductive constituent material of the cathode atone terminal of the electrode group while exposing the conductiveconstituent material of the anode at the other terminal and thenbringing-each material into contact with the cell case.

[0027] In the case of the wound electrode group, the method ofcollecting current involves exposing an electrically conductiveconstituent material of the cathode at one edge face of the electrodegroup (face parallel to the flat plane of the flat cell) while exposingan electrically conductive constituent material of the anode at theother edge face and then bringing the respective exposed electrodeconstituent materials into contact with the cathode and anode cellcases, respectively. According to this structure, the discharge capacitycan be increased without providing any space or insulating plate betweenthe electrode group and the cell case. In addition, because noshort-circuiting occurs between the cell case or the electrode and thetab terminal, the cell is superior in safety and reliability.

[0028] A large number of systems can be used for winding the electrodegroup. In a preferable system, the cathode and the anode, both in asheet form, are wound to be opposite to each other via a separator asshown in FIG. 2. According to this winding system, the electrode fromthe start to the end of winding can be efficiently used. Further, thereis no space in the center of a core of the wound electrodes, so thatwhen a spiral form of the flat electrodes is used, the electrodes can beeffectively utilizable because both the electrodes are opposite to eachother from the start of winding.

[0029] The wound electrode group may be used as such, but after beingwound, it is preferably compressed to improve adhesion of the cathodevia the separator to the anode. In the coin- or button-shaped, flatnon-aqueous electrolyte secondary cell whose internal volume is small,if there is no space in the center of a core of the wound electrodes,the electrodes can be additionally accommodated therein, and further theadhesion of the cathode via the separator to the anode can be improved.The flat electrodes in a spiral form, constructed by bending and windingthe opposing electrodes such that the face where the cathode is oppositethe anode is parallel to the flat plane of the flat cell, followed bycompressing the electrodes, have the advantage that they are firmlywound and excellent in adhesion. Furthermore the above advantage isobtained by sticking any tapes on R part of side of electrode group.

[0030] Furthermore, in the flat cell having such an opening-sealedstructure as in the present invention, stress was applied in theperpendicular direction to the flat plane of the cathode and anode casesupon caulking of the cell case, whereby the adhesion between theelectrode group and the cell case is improved, charge/discharge can beconducted smoothly, and the characteristics of the cell are improved.The exposed portions of the electrode constituent materials of theelectrode group may contact the electrode case directly or electricallyindirectly via a metal foil, a metal net, metal powder, carbon fillersor a conductive coating.

[0031] Now, the electrodes are described. For both the cathode andanode, it is possible to use a conventional method of forming a granulardepolarizing mix for cell or a method of filling a metal substrate suchas metal net or foamed nickel with a depolarizing mix for cell.Preferably, a depolarizing mix for cell in a slurry form is applied ontoa metal foil, then dried and optionally further rolled so that a thinelectrode can be easily prepared. If the electrodes on which thedepolarizing mix for cell containing the active material is applied on ametal foil as described above are used, it is preferable for volumeefficiency that the inner electrodes in the electrode group are thosewherein a layer of the active material is formed on both sides of themetal foil, while the outermost electrodes in the electrode group, thatis, the electrodes in contact with the cell case, are preferably thosewherein particularly the metal foil in the electrode materials isexposed in order to reduce contact resistance. In this case, the activematerial layer may be formed on only one side of the outermostelectrode, or after the active material later is formed on both sides ofthe outermost electrode, the active material layer may be removed fromone side.

[0032] Now, the cathode and anode active materials used in the cell ofthe present invention are described.

[0033] In the present invention, special attention is paid to thestructure of the cell including the electrodes, so there is no limit tothe cathode active materials. It is possible to use metal oxides such asMnO₂, V₂O₅, Nb₂O₅, LiTi₂O₄, Li₄Ti₅O₁₂, LiFe₂O₄, lithium cobaltate,lithium nickelate and lithium manganate, inorganic compounds such asfluorinated graphite and FeS₂, and organic compounds such as polyanilineor polyacene structural compounds. Among these materials, lithiumcobaltate, lithium nickelate, lithium manganate and a mixture thereof,or lithium-containing oxides where such elements are partially replacedby other metal elements are more preferable because of high workingpotential and excellent cycle characteristics, and in the flatnon-aqueous electrolyte secondary cell which may be used for a prolongedperiod of time, lithium cobaltate is most preferable because of highcapacity, low reactivity with an electrolyte or water, and chemicalstability.

[0034] The anode active materials are not particularly limited neither,and it is possible to use metal lithium, lithium alloys such as Li—Al,Li—In, Li—Sn, Li—Si, Li—Ge, Li—Bi and Li—Pb, organic compounds such aspolyacene structural compounds, carbon materials capable of occludingand releasing lithium, oxides such as Nb₂O₅, LiTi₂O₄, Li₄Ti₅O₁₂,Li-containing silicon oxides and Li-containing tin oxides, and nitridessuch as Li₃N. Carbon materials capable of occluding and releasinglithium Li are preferable in respect of excellent cycle characteristics,low working potential and high capacity. Particularly, carbon materialshaving a developed graphite structure wherein the distance of the faced₀₀₂ is 0.338 nm or less, for example natural graphite, artificialgraphite, expanded graphite, calcinated mesophase pitch and calcinatedmesophase pitch fiber are preferable in respect of less reduction in theworking voltage of the cell in the end of discharge.

[0035] In the flat non-aqueous electrolyte secondary cell having anelectrode group in a laminate, wound or bent form as described above,the degree of adhesion between the cathode and anode cell cases and theelectrode group has a significant influence on cell impedance and cellperformance. For example, when the cell is stored for a long time in ahigh-temperature atmosphere at about 60° C., the non-aqueous electrolyteis decomposed, the cell is expanded, the adhesion between the cell caseand the electrode group is significantly worsened, and the performanceof the cell is deteriorated. In addition, when the flat non-aqueouselectrolyte secondary cell is placed in an abnormal state such asshort-circuiting, the cell causes a significant increase in temperature,resulting in decomposition of the non-aqueous electrolyte orgasification of the solvent thereby increasing the inner pressure in thecell to cause the problem of cell breakage.

[0036] This problem was solved in the present invention by usingethylene carbonate (EC) and γ-butyrolactone (GBL) as the major solventfor the non-aqueous electrolyte and lithium borofluoride as thesupporting electrolyte. By this constitution, gas generation can besuppressed even at high temperature to prevent cell breakage.

[0037] A mixed solvent of EC and GBL is stable to a graphitized carbonanode and hardly decomposed at the side of the anode. Further, thestability of the mixed solvent at high potential is also high, and evenif left for a long time in a high-temperature atmosphere, thenon-aqueous electrolyte is hardly decomposed at the side of the cathode,thus hardly generating gas. Further, both EC and GBL have high boilingpoints (about 240° C. and about 200° C., respectively) so that even ifthe cell is heated upon short-circuiting or placed in an abnormalatmosphere at about 150° C., the vapor pressure of the mixed solvent canbe kept low, and its decomposition hardly occurs. Accordingly, theincrease in the inner pressure in the cell and the breakage of the cellcan be prevented.

[0038] In the mixed solvent of EC and GBL, the volume ratio of EC to GBLis preferably 0.3 to 1.0. This is because if the volume ratio of EC istoo low, a protective coating is not sufficiently formed on the surfaceof the carbon material constituting the anode during charge anddischarge, to cause deterioration in cycle characteristics. On the otherhand, if the volume ratio of EC is too high, lithium ion is hardlytransferred in a low-temperature atmosphere to cause deterioration inlow-temperature characteristics.

[0039] Lithium borofluoride is used as the supporting electrolyte forthe following reason. As the supporting electrolyte, LiBF₄, lithiumphosphate hexafluoride (LiPF₆), lithium perchlorate (LiClO₄), lithiumtrifluoromethane sulfonate (LiCF₃SO₃) are used generally used, butlithium borofluoride (LiBF₄) is preferably used for compatibility with agraphitized carbon anode, stability at high potential and stability in ahigh-temperature atmosphere. For example, when the graphitized carbonanode is used as the anode active material and the mixed solvent of ECand GBL is used as the solvent for non-aqueous electrolyte, use of LiPF₆and LiClO₄ causes slight decomposition of the solvent on the anode andis thus not preferable. Use of LiCF₃SO₃ is not preferable either,because its electric conductivity is low and the resulting cell is poorin desired heavy loading discharge characteristics. On the other hand,LiBF₄ though being slightly inferior to LiPF₆ and LiClO₄ in heavyloading discharge characteristics is preferably used becausedecomposition of the solvent can be prevented, and by adding LiBF₄ at aconcentration of 1.3 mol/l to 1.8 mold which is higher than a usualconcentration of 0.5 mol/l to 1.0 mol/l, the resulting cell has improvedheavy loading characteristics, to achieve the same heavy loadingcharacteristics as by LiPF₆ and LiClO₄.

[0040] In the conventional lithium ion secondary cell using a lithiumcobaltate-containing oxide as the cathode active material and a carbonmaterial as the anode, the material contained in the cathode member isdissolved in the electrolyte and precipitated on the surface of theanode during long-term storage, to cause the problem of increasedinternal resistance. To solve this problem, ferrite-based stainlesssteel containing chromium and molybdenum (JP-A 63-124358),austenite-based stainless steel containing chromium and molybdenum (JP-A6-111849) and ferrite-based stainless steel containing molybdenum withan increased amount of chromium (JP-A 2-126554) have been proposed ascathode case materials. However, in the non-aqueous electrolyte cellshaving a cell voltage of 4 V or more, the cathode member even using suchstainless steel cannot be completely prevented from being dissolvedduring storage.

[0041] To solve this problem, the present invention comprises use ofstainless steel comprising 0.1 to 0.3% niobium, 0.1 to 0.3% titanium and0.05 to 0.15% aluminum contained in ferrite-based stainless steelcontaining 28.50 to 32.00% chromium and 1.50 to 2.50% molybdenum in thecathode case or as a member constituting a metallic part broughtdirectly into contact with the cathode active material. Further, thisinvention comprises use of stainless steel comprising 0.8 to 0.9%niobium, 0.05 to 0.15% titanium and 0.20 to 0.30% copper contained inferrite-based stainless steel containing 20.00 to 23.00% chromium and1.50 to 2.50% molybdenum. By use of such stainless steel, the cathodemember can be prevented from being dissolved during long-term storage.

[0042] When these flat non-aqueous electrolyte secondary cells areintegrated in devices, lead terminals are often welded by resistancewelding into cathode and anode cases and then attached via a solder to adevice. In this case, the above-described flat non-aqueous electrolytesecondary cell, the electrode group comprises a cathode and an anode asthin as 1 mm or less and a polyethylene or polypropylene thin filmseparator of 0.5 mm or less laminated or wound therein, where thecathode and anode are brought directly into contact with cathode andanode cases respectively. Accordingly, if a voltage of about 500 V isapplied across the cell cases, the heat generated upon welding istransmitted through the cell cases to reach the electrodes and separatorto cause shrinkage or generate holes in the separator, resulting indeterioration in the capacity and short-circuiting in the cell. Inaddition, the voltage is directed to the welded portion, so that theelectrode connected to the welded portion is removed from thecurrent-collecting body, thus causing deterioration in the functions ofthe cell. This problem is solved when welding power is lowered, butbecause of poor welding strength, there arises another problem of theremoval of lead terminals or the poor contact between the cell and leadterminals. Even if the lead terminals are welded by laser welding, heatevolution cannot be prevented and similar problems may be caused.

[0043] To prevent such problems, a metal net may be provided between thecathode case or the anode case and the electrode group. By doing so,heat generated upon welding of the lead terminals can be dissipatedthereby preventing breakage of the electrodes and separator in the cellcase.

[0044] To prevent the problems described above, there also is a methodof arranging a non-metallic thermal insulator between the cathode caseor the anode case and the thin-film separator. By doing so, thetransmission of heat generated upon welding of the lead terminals to theelectrode group in the cell can be blocked so that the breakage of theelectrodes and separator in the cell can be prevented. To install thisthermal insulator, it is preferable that the current-collecting bodywhich in the electrode group, is brought into contact with the cell caseis formed in a “U” shape, and said thermal insulator is kept in thisU-shaped current-collecting body. According to this method, the objectcan be achieved without making the structure complicated.

[0045] Preferably, the metal net is shaped to form a space in the cellcase in order to incorporate an electrolyte into the space. The metalnet includes e.g. a metal net, expanded metal, punched metal and foam.The electrolyte in this space also works for dissipating heat andvoltage. There is no particular limit to the shape of thecurrent-collecting body and the form of the opening thereof.

[0046] With respect to the thickness of the metal net, this thicknessplus the thickness of the can used is important. As their thickness isreduced, the effect of dissipating heat is decreased, thus failing toachieve the object. On the other hand, if their thickness is large, heatcan be dissipated, but a large number of electrodes cannot be integratedin the cell, thus leading to a reduction in cell capacity.

[0047] Accordingly, the thickness of the cathode or anode case and themetal net in total is suitably 0.30 to 0.45 mm.

[0048] Preferably, the metal net is previously welded into the internalsurface of the cell case thereby improving adhesion to achieve excellentelectric conductivity. The material of the metal net is not particularlylimited. However, when an active material e.g. a metal oxide having highpotential is used as the cathode, a metal net having a poorerdissolution potential than that of the cathode active material causesthe cell to be deteriorated due to high potential during storage, thusaffecting the performance of the cell. Accordingly, the metal net at theside of the cathode is preferably aluminum, titanium, or stainless steelcontaining a relatively large amount of chromium or molybdenum. Themetal net at the side of the anode is considerably poorer in potentialthan the cathode, thus making the particular attention paid to thecathode unnecessary. Materials in the anode include e.g. stainlesssteel, nickel, copper etc. Further, the surface of the metal net ispreferably coated with a conductive coating in order to lower thecontact resistance between the electrode group and the metal net.

[0049] In the method of arranging a thermal insulator between the caseand the separator, the following thermal insulators are preferably usedfor their stability to the electrolyte and lithium ion: a non-metallicthermal insulator such as glassy material, or a resin selected fromfluoride resins such as polytetrafluoroethylene (PTFE),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-ethylene copolymer (ETFE),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) andpolyvinylidene fluoride (PVDF), polyimide, liquid crystal polymer (LCP),polyphenylene sulfide (PPS), polybutylene terephthalate (PBT),polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP),polyvinyl chloride (PVC), and acetate resin. A thermal insulator havingresistance to a temperature of 150° C. or more is more preferable so asto prevent the thermal insulator from being melted due to heating uponwelding of terminals, thus exerting no adverse effect on the performanceof the cell. The glassy material and a resin selected from fluorineresins such as PTFE, FEP, ETFE, PFA and PVDF, polyimide, LCP, PPS, andPBT are more preferable.

[0050] The thermal insulator is preferably in the form of a flexiblematerial such as film, fabric, nonwoven fabric and fiber, to bring aboutgood adhesion to the current-collecting member in the electrodes as wellas high thermally insulating effect. Further, these materials are usedas the substrate in a tape form preferably provided with an adhesive onone or both sides thereof, thus effectively preventing dislocation ofthe current-collecting member and the thermal insulator. Although theshape of the insulating material is not particularly limited, the areathereof is preferably larger than the area of the current-collectingportion in the electrode group so that in welding of terminals, a highdegree of freedom can be achieved for the position and direction of theterminals.

[0051] When the thermal insulator is too thin, the effect of heatinsulation is insufficient thus failing to achieve the object. On theother hand, when it is too thick, the amount of the active materialcapable of being integrated in the cell is decreased, resulting in areduction in cell capacity. Accordingly, the thickness of the thermalinsulator is preferably 0.05 to 0.2 mm.

[0052] In the flat non-aqueous electrolyte secondary cell of the presentinvention, the area of the electrodes is large to generate largeelectric current so that in unforeseen circumstances such as internalshort-circuiting and excessive discharge, gas is generated in a largeamount, which may lead to breakage. In the structure of the cell,however, a breakage-preventing device such as a safety element in theconventional cylindrical cell cannot be installed. Accordingly, when gasis generated in a too large amount, the cell may be broken to permit thecell content and the vessel to be scattered, which may result in notonly damaging a device using the cell but also harming the human body.

[0053] The flat non-aqueous electrolyte secondary cell of the presentinvention can use the following constitution thereby preventing thebreakage of the cell and improving safety. That is, the cell is providedwith a cutting at the side of the cathode case. Even if it is providedwith a cutting, the insulating packing is compressed in a normal statein the direction of diameter and the direction of height, thuspreventing leakage of the electrolyte; however, upon an increase in theinternal pressure due to uncontrolled heating, the insulating gasket isreleased through the cutting, and the breakage can thereby be prevented.

[0054] To prevent the breakage of the cell certainly upon uncontrolledheating and to prevent inconveniences such as leakage of the electrolytefrom the cell in a normal state, it is preferable that the width of acutting provided at the side of the cathode case has a central angle of0.1 π to 0.9 πrad to the circumference of the cathode case, the depth ofthe cutting is 5 to 30% of the height of the cathode case, as shown inthe experiment described below.

[0055] Further, in the present invention, a lengthwise groove is formedin the opening-sealed portion in the cathode vessel to form a thin-plateportion, so that when an abnormal gas is generated in the cell toincrease the internal pressure, the gas can be discharged therethroughto the outside of the cell. That is, by the increase in the internalpressure, the lengthwise-groove thin-plate portion in the opening-sealedportion in the cathode vessel is pushed up by the anode vessel, wherebythe lengthwise-groove thin-plate portion is deformed and broken to causethe anode vessel to be opened like a bivalve, thus discharging the gasto the outside of the cell. Accordingly, the breakage of the cell bywhich the anode vessel is separated from the main body of the cell thusscattering the cell content can be prevented.

[0056] Further, in the present invention, one or more shattering grooveshaving a concave shape in section can be formed in the anode case inorder to prevent the breakage of the cell in the same way as above. Bydoing so, even if the cell is placed in abnormal circumstances due toe.g. the misuse of the cell, the breakage or explosion thereof can beprevented by opening the above-described shattering grooves. Further,the shattering grooves having a concave shape in section are provided inthe anode case and thus not affected by the electrolyte and the cathodeactive material (oxidizing agent), so they are not corroded. Preferably,the shattering grooves described above are formed on the externalsurface of the anode case in order to work normally even if the cell isplaced in abnormal circumstances.

[0057] In the flat non-aqueous electrolyte secondary cell describedabove, the volume of the active material is significantly changed uponcharge and discharge, and upon discharge, the electrode group is shrunkto fail to keep contact with the cell vessel so that the internalresistance is increased to cause a reduction in voltage upon dischargeof large electric current. To prevent this problem in the invention, theinternal surface of the cathode case and/or the anode case can beprovided with unevenness or protrusions. The dimension of the protrusionis 0.2 to 2.0 mm in diameter and 0.01 to 0.50 mm in height in order toachieve the satisfactory effect. The number of protrusions may be 1 ormore. In place of protrusions, unevenness may be provided by embossing.

[0058] The cell of the present invention has been described mainly byreference to the coin- or button-shaped, flat cell wherein the outermostdiameter of the cell is longer than the height of the cell, but the cellof the present invention is not limited to such an example and can beapplied similarly to flat cells of unique elliptic or rectangular shape.

EXAMPLES

[0059] Hereinafter, the present invention is described in more detail byreference to the Examples and Comparative Examples.

Example 1

[0060] A process for producing the cell of the present invention inExample 1 is described by reference to the sectional drawing in FIG. 1.

[0061] First, 5 parts by weight of acetylene black and 5 parts by weightof graphite powder were added as electrically conductive agents to 100parts by weight of LiCoO₂, and 5 parts by weight of polyvinylidenefluoride was added as a binding agent, and these materials were dilutedwith N-methyl pyrrolidone and mixed to give a cathode mix for cell in aslurry form. Then, this cathode mix was applied with a doctor blade ontoone side of an aluminum foil of 0.02 mm in thickness as a cathodecurrent-collecting body 2 a, followed by drying it. This procedure ofapplication and drying was repeatedly conducted until the thickness ofthe resulting coating of the active material-containing layer reached0.39 mm, whereby the cathode active material-containing layer 2 b wasformed on one side of the aluminum foil to prepare a single-coatedcathode.

[0062] Then, both sides of an aluminum foil were coated with the cathodemix in the same manner as above until the thickness of the resultingcoating of the active material-containing layer on each side reached0.39 mm, to prepare a double-coated cathode.

[0063] Then, 2.5 weight parts each of styrene butadiene rubber (SBR) andcarboxymethyl cellulose (CMC) were added as binding agents to 100 partsby weight of graphitized mesophase pitch carbon fiber powder, thendiluted with de-ionized water and mixed to give an anode mix for cell ina slurry form. This anode mix for cell was repeatedly applied and driedon a copper foil of 0.02 mm in thickness as an anode current-collectingbody 4 a, to form an active material-containing layer 4 b of 0.39 mm inthickness, whereby a single-coated anode was prepared.

[0064] Then, both sides of a copper foil were coated in the same manneras for this single-coated anode until the thickness of the coating ofthe anode active material-containing layer on each side reached 0.39 mm,to prepare a double-coated anode.

[0065] These electrodes were cut into square pieces of 13 mm in widthand 13 mm in length having a protrusion of 6 mm in width and 2 mm inlength on one edge thereof, and then the active material-containinglayer formed on this protrusion was removed to expose the aluminum foilor copper foil as an electrically connecting portion, whereby squaredouble- and single-coated cathode and anode plates of 13 mm in width and13 mm in length having the active material-containing layer formedthereon were prepared.

[0066] Then, the cathode active material-containing layer formed on thesingle-coated cathode plate was arranged to face the double-coated anodeplate via separator 3 consisting of a polyethylene fine-porous membraneof 25 μm in thickness, such that the electrically connecting portion inthe anode was positioned in the opposite side to the electricallyconnecting portion in the cathode plate. Then, the double-coated cathodeplate was installed such that its electrically connecting portion wasdirected in the same direction as the previously arranged cathode plate,followed by arranging another single-sided anode plate opposite thedouble-coated cathode plate via separator 3 such that the anode activematerial-containing layer 4 b on the single-coated anode plate wasbrought into contact with the separator, while the electricallyconnecting portion in the single-coated anode plate was directed in thesame direction as the electrically connecting portion in the previouslyarranged anode plate. In this manner, the electrode group shown in FIG.1 is constructed. That is, in this drawing, all the electricallyconnecting portions in the cathodes are exposed from the left of theelectrode group, while all the electrically conductive portions in theanodes are exposed from the right of the electrode group, and therespective exposed electrically connecting portions are electricallyconnected.

[0067] The electrode group thus constructed was dried at 85° C. for 12hours, and the uncoated side (that is, the anode current-collecting body4 a) of the single-coated anode plate in the electrode group wasarranged to be brought into contact with the internal bottom of theanode metal case 5 having the insulating gasket 6 (opening diameter, 20mm; opening area, 3.14 cm) integrated therein. Then, a non-aqueouselectrolyte prepared by dissolving 1 mol/l LiPF₆ as supportingelectrolyte in a mixed solvent consisting of ethylene carbonate andmethyl ethyl carbonate in a volume ratio of 1:1 was injected into it.Further, the stainless steel cathode case 1 was fit thereto so as to bebrought into contact with the uncoated side (that is, the cathodecurrent-collecting body 2 a) of the single-coated cathode plate in theelectrode group. After the resulting cell was turned upside down, thecathode case was caulked to seal the opening, to construct the flatnon-aqueous electrolyte secondary cell of 3 mm in thickness and 24.5 mmin diameter shown in FIG. 1. The number of faces where a cathode wasopposite an anode via a separator is 3 in total, and the total sum ofthe areas of the opposing cathodes and anodes is 5.1 cm².

Example 2

[0068] A cell was constructed in the same manner as in Example 1 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.22 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 2. The number of faceswhere a cathode was opposite an anode via a separator is 5 in total, andthe total sum of the areas of the opposing cathodes and anodes is 8.5cm².

Example 3

[0069] A cell was constructed in the same manner as in Example 1 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.15 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 3. The number of faceswhere a cathode was opposite an anode via a separator is 7 in total, andthe total sum of the areas of the opposing cathodes and anodes is 11.8cm².

Example 4

[0070] A cell was constructed in the same manner as in Example 1 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.11 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 4. The number of faceswhere a cathode was opposite an anode via a separator is 9 in total, andthe total sum of the areas of the opposing cathodes and anodes is 15.2cm².

Comparative Example 1

[0071] Comparative Example 1 is described by reference to FIG. 4.

[0072] Five parts by weight of acetylene black and 5 parts by weight ofgraphite powder were added as electrically conductive agents to 100parts by weight of LiCoO₂, and 5 parts by weight of polyethylenetetrafluoride was added as a binding agent, and these materials weremixed and ground to give a cathode mix for cell in a granular form.Then, this cathode mix was compression-molded into a cathode tablet 12having a diameter of 19 mm and a thickness of 1.15 mm.

[0073] Then, 2.5 weight parts each of styrene butadiene rubber (SBR) andcarboxymethyl cellulose (CMC) were added as binding agents to 100 partsby weight of graphitized mesophase pitch carbon fiber powder, thenmixed, dried and ground to give an anode mix for cell in a granularform. This anode mix was compression-molded into an anode tablet 14having a diameter of 19 mm and a thickness of 1.15 mm.

[0074] Then, these positive and anode tablets were dried at 85° C. for12 hours. The anode tablet 14, the separator 13 made of a polypropylenenon-woven fabric of 0.2 mm in thickness, and the cathode tablet 12 werearranged in this order in an anode case 5 having an insulating gasket 6with an opening area of 3.14 cm² integrated therein. Then, a non-aqueouselectrolyte prepared by dissolving 1 mol/l LiPF₆ as supportingelectrolyte in a mixed solvent of ethylene carbonate and methyl ethylcarbonate in a volume ratio of 1:1 was injected into it. Further, thestainless steel cathode case 1 was fit thereto, and after the resultingcell was turned upside down, the cathode case was caulked to construct aflat non-aqueous electrolyte secondary cell of 3 mm in thickness and24.5 mm in diameter. The number of faces where a cathode was opposite ananode via a separator is 1 in total, and the total sum of the areas ofthe opposing cathode and anode is 2.8 cm².

Comparative Example 2

[0075] A single-coated cathode and a single-coated anode each having acoated active material-containing layer of 1.24 mm in thickness wereprepared in the same manner as in Example 1 and arranged to be oppositeto each other via a separator such that the active material layer wasplaced in the side of the separator, and a cell was prepared in the samemanner as in Example 1. Accordingly, the number of faces where a cathodewas opposite an anode via a separator is 1 in total, and the total sumof the areas of the opposing cathode and anode is 1.7 cm².

[0076] The cells thus prepared in the Examples and the ComparativeExamples were initially charged for 48 hours at a constant current of 3mA at a constant voltage of 4.2 V. Thereafter, the cells were dischargedat a constant current of 30 mA until 3.0 V to determine theirheavy-loading discharge capacity. The results are shown in Table 1.TABLE 1 thickness sum of heavy-loading of active number of cathode-anodedischarge kind of material-containing cathode-anode areas capacityelectrodes layer(mm) faces (cm²) (mAh) comp. tablet 1.15 1 2.8 6.4examp.1 electrode comp. coated 1.24 1 1.7 2.4 examp.2 electrode example1 coated 0.39 3 5.1 22.8 electrode example 2 coated 0.22 5 8.5 52.7electrode example 3 coated 0.15 7 11.8 53.7 electrode example 4 coated0.11 9 15.2 52.5 electrode

[0077] As is evident from Table 1, the cells in the Examples have asignificantly larger discharge capacity upon heavy discharge than thecell in Comparative Example 1 (wherein a tablet-shaped electrodeprepared by the conventional method of forming a granular depolarizingmix for cell is used and the area where the cathode is opposite theanode is smaller than the area of the opening of the gasket) and thecell in Comparative Example 2 (wherein the number of faces where acathode is opposite an anode is only 1, and the area where the cathodeis opposite the anode is smaller than the area of the opening of thegasket).

[0078] In the Examples of this invention, the flat non-aqueous solventsecondary cell wherein a non-aqueous solvent was used as the non-aqueouselectrolyte, but as a matter of course, these examples can also beapplied to polymer secondary cells using a polymer electrolyte as thenon-aqueous electrolyte or to solid electrolyte secondary cells using asolid electrolyte. Further, a polymer thin film or solid electrolytefilm can also be used in place of the resin separator. The cellsdescribed above are mainly coin-shaped wherein the opening was sealed bycaulking the cathode case, but the cathode and anode may be exchanged sothat the opening of the anode case is sealed by caulking. Further, theshape of the cell may not be necessarily round, and the presentinvention can also be applied to flat non-aqueous electrolyte secondarycells of unique elliptic or rectangular shape.

[0079] Now, examples of the cells of this invention having a wound cell(electrode) group are described.

Example 5

[0080]FIG. 2 is a sectional drawing of the cell of the present inventionin Example 5.

[0081] Hereinafter, a process for producing the cell in Example 5 isdescribed.

[0082] First, 5 parts by weight of acetylene black and 5 parts by weightof graphite powder were added as electrically conductive agents to 100parts by weight of LiCoO₂, and 5 parts by weight of polyvinylidenefluoride was added as a binding agent, and these materials were dilutedwith N-methyl pyrrolidone and mixed to give a cathode mix for cell in aslurry form. Then, this cathode mix was applied with a doctor blade ontoone side of an aluminum foil of 0.02 mm in thickness as a cathodecurrent-collecting body, followed by drying it. This procedure ofapplication and drying was repeatedly conducted until the thickness ofthe resulting coating of the cathode active material-containing layerreached 0.15 mm, whereby the cathode active material-containing layer 2b was formed on one side of the aluminum foil. Then, the activematerial-containing layer on a portion 10 mm apart from the edge wasremoved from the surface of this electrode body, whereby the aluminumlayer was exposed to form an electrically connecting portion. Then, theelectrode body was cut into pieces of 15 mm in width and 120 mm inlength to prepare a cathode plate.

[0083] Then, 2.5 weight parts each of styrene butadiene rubber (SBR) andcarboxymethyl cellulose (CMC) were added as binding agents to 100 partsby weight of graphitized mesophase pitch carbon fiber powder, thendiluted with de-ionized water and mixed to give an anode mix for cell ina slurry form. This anode depolarizing mix was repeatedly applied anddried in the same manner as for the cathode, on a copper foil of 0.02 mmin thickness as an anode current-collecting body, to form an activematerial-containing layer 4 b of 0.15 mm in thickness, whereby adouble-coated anode was prepared. Then, the active material-containinglayer on a portion 10 mm apart from the edge was removed from one sideof this electrode body, whereby the copper layer was exposed to form anelectrically connecting portion. Then, the electrode body was cut intopieces of 15 mm in width and 120 mm in length to prepare an anode plate.

[0084] Then, the cathode and the anode were wound in a spiral form viaseparator 3 consisting of a polyethylene fine-porous film of 25 μm inthickness such that the wound electrode group ended in the cathode andanode electrically connecting portions in the outer periphery. Theelectrode group thus prepared was pressurized in such a direction thatthe face where the cathode was opposite the anode was parallel to theflat plane of the flat cell. The electrode group was pressurized toeliminate a space in the center of the wound electrodes. The total sumof the area of the face where the cathode was opposite the anode via theseparator in this cell is 34.5 cm².

[0085] The electrode group thus constructed was dried at 85° C. for 12hours, and the uncoated side of the single-coated anode plate in theelectrode group, was arranged to be brought into contact with theinternal bottom of the anode metal case 5 having the insulating gasket 6with an opening diameter of 20 mm and an opening area of 3.14 cm²integrated therein. Then, a non-aqueous electrolyte prepared bydissolving 1 mol/l LiPF₆ as supporting electrolyte in a mixed solventconsisting of ethylene carbonate and methyl ethyl carbonate in a volumeratio of 1:1 was injected into it. Further, the stainless steel cathodecase 1 was fit thereto so as to be brought into contact with theuncoated side of the single-coated cathode plate in the electrode group.After the resulting cell was turned upside down, the cathode case wascaulked to seal the opening, to construct the flat non-aqueouselectrolyte secondary cell of 3 mm in thickness and 24.5 mm in diameterin Example 5.

Example 6

[0086] A cell was prepared in the same manner as in Example 5 exceptthat the cathode and the anode, both in a sheet form, were spirallywound via a separator and simultaneously bent at predetermined intervalssuch that that the face where the cathode was opposite the anode wasparallel to the flat plane of the flat cell.

[0087] The cells in the Examples 5 and 6 and Comparative Example 1 wereinitially charged for 48 hours at a constant current of 3 mA at aconstant voltage of 4.2 V. Thereafter, the cells were discharged at aconstant current of 30 mA until 3.0 V to determine their dischargecapacity. The results are shown in Table 2. TABLE 2 discharge capacityat number of 30mA cathode-anode constant kind of faces currentelectrodes (cm²) (mAh) example 5 coated electrode 34.5 51.9 example 6coated electrode 34.5 52.7 comp. examp. 1 tablet electrode 2.8 6.4

[0088] As is evident from Table 2, the cells of this invention inExamples 5 and 6 have a significantly larger discharge capacity thanthat of the cell in Comparative Example 1 (wherein a tablet-shapedelectrode prepared by the conventional method of forming a granulardepolarizing mix for cell is used and the area where the cathode isopposite the anode is smaller than the area of the opening of thegasket). For the winding system, the system of spirally winding theelectrodes while bending them as shown in Example 2 is superior incurrent collection between the electrode layers and heavy loadingcharacteristics.

[0089] In the examples described above, the flat non-aqueous solventsecondary cell wherein a non-aqueous solvent was used in the non-aqueouselectrolyte, but as a matter of course, these examples can also beapplied to polymer secondary cells using a polymer electrolyte as thenon-aqueous electrolyte or to solid electrolyte secondary cells using asolid electrolyte. Further, a polymer thin film or solid electrolytefilm can also be used in place of the resin separator. The cell wasdescribed above is mainly coin-shaped wherein the opening was sealed bycaulking the cathode case, but the cathode and anode may be exchanged sothat the opening of the anode case is sealed by caulking. Further, theshape of the cell may not be necessarily coin-shaped, and the presentinvention can also be applied to flat non-aqueous electrolyte secondarycells of unique elliptic or rectangular shape.

[0090] Now, examples of the cells of this invention wherein anopening-sealing plate was used in place of the insulating gasket toclose the opening are described.

Example 7

[0091] A process for producing the cell in this example is described byreference to the sectional drawing in FIG. 3.

[0092] Double-coated and single-coated cathode and anode plates havingthe same dimension were constructed in the same manner as in Example 1.Then, these cathode and anode plates were used to construct an electrodegroup in the same manner as in Example 1.

[0093] The electrode group thus constructed was dried at 85° C. for 12hours, and by use of this electrode group, the flat non-aqueouselectrolyte secondary cell shown in FIG. 3 was constructed in thefollowing manner. That is, the uncoated side (that is, the cathodecurrent-collecting body 2 a) of the single-coated cathode plate in theelectrode group was arranged to be brought into contact with theinternal bottom of the cathode case 11 having an opening diameter of 20mm and an opening area of 3.14 cm², which had been insulated byapplication of SBR onto the internal surface thereof. Then, anon-aqueous electrolyte prepared by dissolving 1 mol/l LiPF₆ assupporting electrolyte in a mixed solvent consisting of ethylenecarbonate and methyl ethyl carbonate in a volume ratio of 1:1 wasinjected into it.

[0094] The anode terminal 8 which was electrically integrated in thecurrent-collecting plate 10 is arranged in the center of theopening-sealed plate 7, and the uncoated side (that is, the anodecurrent-collecting body 4 a) of the single-coated anode plate in theelectrode group is brought into contact with the current-collectingplate 10. The anode terminal 8 and the opening-sealed plate 7 areelectrically insulated by the glass seal 9. The cathode case 11 and theopening-sealed plate 7 are sealed by laser welding to construct a flatnon-aqueous electrolyte secondary cell of 5 mm in height and 21.0 mm indiameter. The number of faces where a cathode was opposite an anode viaa separator is 3 in total, and the total sum of the areas of theopposing cathodes and anodes is 5.1 cm².

Example 8

[0095] A cell was constructed in the same manner as in Example 7 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.22 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 2. The number of faceswhere a cathode was opposite an anode via a separator is 5 in total, andthe total sum of the areas of the opposing cathodes and anodes is 8.5cm².

Example 9

[0096] A cell was constructed in the same manner as in Example 7 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.15 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 3. The number of faceswhere a cathode was opposite an anode via a separator is 7 in total, andthe total sum of the areas of the opposing cathodes and anodes is 11.8cm².

Example 10

[0097] A cell was constructed in the same manner as in Example 7 exceptthat the coating of the active material-containing layer in each of thecathode and anode in the electrode group was 0.11 mm in thickness on oneside, and the number of double-coated cathodes or double-coated anodeslaminated internally in the electrode group was 4. The number of faceswhere a cathode was opposite an anode via a separator is 9 in total, andthe total sum of the areas of the opposing cathodes and anodes is 15.2cm².

Comparative Example 3

[0098] Cathode and anode tablets were prepared in the same manner as inComparative Example 1 and dried at 85° C. for 12 hours. As shown in FIG.5, the cathode tablet 12, the separator 13 and the anode tablet 14 werearranged in this order on the internal bottom of the same cathode case11 as in Example 7, and the same non-aqueous electrolyte as in Example 7was injected into it. The cathode case 11 and the opening-sealed plate 7were sealed by laser welding to construct the flat non-aqueouselectrolyte secondary cell of 5 mm in thickness and 21.0 mm in diametershown in FIG. 5.

[0099] In FIG. 5, the same symbols are used to refer to the same membersin FIG. 3. The number of faces where a cathode was opposite an anode viaa separator is 1 in total, and the total sum of the areas of theopposing cathode and anode is 2.8 cm².

Comparative Example 4

[0100] A cell was constructed in the same manner as in Example 7 exceptthat the electrode group consisted of one cathode and one anode, both ofwhich were single-coated electrodes, and the thickness of the coatedactive material-containing layer for each electrode was 1.24 mm. Thenumber of faces where a cathode was opposite an anode via a separator is1 in total, and the total sum of the areas of the opposing cathode andanode is 1.7 cm².

[0101] The respective cells thus constructed in Examples 7 to 10 andComparative Examples 3 to 4 were initially charged for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V. Thereafter, thecells were discharged at a constant current of 30 mA until 3.0 V todetermine their heavy loading discharge capacity. The results are shownin Table 3. TABLE 3 thickness number heavy-loading of active of sum ofdischarge kind of material-containing cathode-anode cathode-anodecapacity electrodes layer(mm) faces areas (cm²) (mAh) comp. tablet 1.151 2.8 6.4 examp.3 electrode comp. coated 1.24 1 1.7 2.4 examp.4electrode example 7 coated 0.39 3 5.1 22.8 electrode example 8 coated0.22 5 8.5 52.7 electrode example 9 coated 0.15 7 11.8 53.7 electrodeexample coated 0.11 9 15.2 52.5 10 electrode

[0102] As is evident from Table 3, the respective cells in the Examplesabove have a significantly larger discharge capacity upon heavy-loadingdischarge than the cell in Comparative Example 3 using tablet-shapedelectrodes prepared by the conventional method of forming a granular mixfor cell or than the cell in Comparative Example 4 wherein the number offaces where a cathode was opposite an anode was only 1 and thus the areaof the opposing cathode and anode was small.

[0103] In the examples described above, the flat non-aqueous solventsecondary cell wherein a non-aqueous solvent was used in the non-aqueouselectrolyte, but as a matter of course, these examples can also beapplied to polymer secondary cells using a polymer electrolyte as thenon-aqueous electrolyte or to solid electrolyte secondary cells using asolid electrolyte. Further, a polymer thin film or solid electrolytefilm can also be used in place of the resin separator. The cathode andanode may be exchanged. Further, the shape of the cell may not benecessarily round, and the present invention can also be applied to flatnon-aqueous electrolyte secondary cells of unique elliptic orrectangular shape.

[0104] Now, the examples where the electrolyte was examined aredestribed.

[0105] A. Experiment on the Type of Solvent of Non-Aqueous Electrolyte

Example 11

[0106] A flat non-aqueous electrolyte secondary cell was constructed inthe same manner as in Example 5 except that a non-aqueous electrolytecontaining 1.5 mol/l LiBF₄ as a supporting electrolyte dissolved in amixed solvent of GBL and EC in a ratio of 2:1 was injected into the cellin Example 5.

Comparative Example 5

[0107] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of diethyl carbonate(DEC) and EC in a ratio of 2:1 was injected.

Comparative Example 6

[0108] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of methyl ethylcarbonate (MEC) and EC in a ratio of 2:1 was injected.

[0109] The thus constructed cells in Example 11, Comparative Examples 5and 6 were initially charged for 48 hours at a constant current of 3 mAat a constant voltage of 4.2 V Thereafter, the cells were examined underthe following conditions, that is, in a test of high-temperature storagecharacteristic 1, a heating test and a short-circuiting test to examinethe characteristics of the cells. The results are shown in Table 4.

[0110] Initial Discharge Capacity

[0111] The cell was discharged at a constant current of 30 mA in anatmosphere at 20° C., to determine the capacity of discharge until thevoltage in the closed circuit became 3.0 V

[0112] High-Temperature Storage Characteristic 1

[0113] The cell in a charged state was stored for 30 days in anatmosphere at 60° C., and the cell was measured for its height and thendischarged at a constant current of 30 mA in an atmosphere at 20° C., todetermine the capacity of discharge until the voltage in the closedcircuit became 3.0 V The capacity (%) after high-temperature storage,relative to the initial discharge capacity, is shown in Table 4.

[0114] Heating Test

[0115] The cells in a charged state were heated to 150° C. at anincreasing temperature of 5° C./min., and the cells were kept at 150° C.for 3 hours and then examined for their state. The number of brokencells in this test is shown in Table 4.

[0116] Short-Circuiting Test

[0117] The cells in a charged state were short-circuited by connectingthe cathode terminal to the anode terminal via a copper wire having asectional area of 1.3 mm². The number of broken cells in this test isshown in Table 4. TABLE 4 high-temperature number of broken number ofbroken storage cell/all tested cell/all tested cell non-aqueouscharacteristics 1 cell at heating at short-circuiting electrolyte (%)test test example 11 1.5 mol/LiBF₄ EC/GBL 84  0/10 0/10 comp. examp. 51.5 mol/LiBF₄ EC/DEC 42  9/10 8/10 comp. examp. 6 1.5 mol/LiBF₄ EC/MEC44 10/10 7/10

[0118] As can be seen from Table 4, when the mixed solvent of DEC and ECor the mixed solvent of MEC and EC was used as the solvent, the cellundergoes in deterioration in capacity after storage at hightemperatures, and when subjected to the heating test or short-circuitingtest, the cell is broken. On the other hand, it was found that when themixed solvent of GBL and EC is used as the solvent, the cell is hardlydeteriorated after storage at high temperatures, and when subjected tothe heating test or short-circuiting test, the cell is not broken.

[0119] B. Experiment for Examination of Characteristics on the VolumeMixing Ratio of GBL and EC

Example 12

[0120] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of GBL and EC in aratio of 10:3 was injected.

Example 13

[0121] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of GBL and EC in aratio of 1:1 was injected.

Reference Example 1

[0122] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of GBL and EC in aratio of 10:1 was injected.

Reference Example 2

[0123] A cell was constructed in the same manner as in Example 5 exceptthat a non-aqueous electrolyte containing 1.5 mol/l LiBF₄ as asupporting electrolyte dissolved in a mixed solvent of GBL and EC in aratio of 2:3 was injected.

[0124] The thus constructed 10 cells in each of Examples 11, 12 and 13and Reference Examples 1 and 2 were initially charged for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V. Thereafter, thecells were examined for their initial discharge capacity in the samemanner as in Experiment A and then for their discharge capacity in alow-temperature atmosphere and cycle characteristics as shown below, toexamine the characteristics of the cells. The results are shown in Table5.

[0125] Discharge Capacity in a Low Temperature Atmosphere

[0126] The cells were discharged at a constant current of 30 mA in anatmosphere at −30° C., to examine the capacity of discharge until thevoltage in the closed circuit became 3.0 V The degree of utilization,relative to the initial discharge capacity, is shown in Table 5.

[0127] Cycle Characteristics

[0128] The cell was discharged at a constant current of 30 mA in anatmosphere at 20° C., to measure the capacity of discharge until thevoltage in the closed circuit became 3.0 V. Thereafter, the cell wascharged for 3 hours at a constant current of 30 mA at a constant voltageof 4.2 V. The cell was subjected to 100 cycles of this discharge andcharge. The discharge capacity (%) in the 100th cycle, relative to theinitial discharge capacity, is shown in Table 5. TABLE 5 degree ofutilization at cycle non-aqueous ratio of a low temperaturecharacteristics electrolyte EC/GBL (%) (%) ref. examp. 1 1.5 mol/LiBF₄EC/GBL 0.1 83 68 example 12 0.3 81 80 example 11 0.5 80 81 example 131.0 79 83 ref. examp. 2 1.5 48 83

[0129] As can be seen from Table 5, when the ratio of EC to GBL is high(Reference Example 2), the low-temperature characteristic is lowered,while when the ratio of EC is low (Reference Example 1), the cyclecharacteristics are lowered. This is because a reduction in the mixingratio of EC leads to insufficient formation of a protective coating onthe surface of the carbon material constituting the anode, thuspermitting decomposition of BGL.

[0130] On the other hand, the cells in the Examples above are superiorin low-temperature characteristic and cycle characteristics.

[0131] C. Experiment on the Type of Supporting Electrolyte inElectrolyte

Comparative Example 7

[0132] A cell was prepared in the same manner as in Example 11 exceptthat the supporting electrolyte in the non-aqueous electrolyte wasLiPF₆.

Comparative Example 8

[0133] A cell was prepared in the same manner as in Example 11 exceptthat the supporting electrolyte in the non-aqueous electrolyte wasLiClO₄.

Comparative Example 9

[0134] A cell was prepared in the same manner as in Example 11 exceptthat the supporting electrolyte in the non-aqueous electrolyte wasLiCF₃SO₃.

[0135] The thus constructed cells in Example 11, Comparative Examples 7to 9 were initially charged for 48 hours at a constant current of 3 mAat a constant voltage of 4.2 V Thereafter, their initial dischargecapacity was confirmed in the same manner as in Experiment A, and thenthe cells were examined under the following conditions to determinetheir high-temperature storage characteristic 2 and heavy-loadingdischarge capacity in order to examine the characteristics of the cells.The results are shown in Table 6.

[0136] High-Temperature Storage Characteristic 2

[0137] The cell in a charged state was stored for 30 days in anatmosphere at 60° C., and the height of the cell was measured. Theincrease (%) of the height, relative to the height before storage, wasdetermined. Thereafter, the cell was discharged at a constant current of30 mA in an atmosphere at 20° C., to determine the capacity of dischargeuntil the voltage in the closed circuit became 3.0 V. The increase (%)of the height of the cell and the capacity (%) after high-temperaturestorage relative to the initial discharge capacity are shown in Table 6.

[0138] Heavy-Loading Discharge Capacity

[0139] The cell was subjected to heavy-loading discharge at a constantcurrent of 180 mA in an atmosphere at 20° C., to determine theheavy-loading discharge capacity until the voltage in the closed circuitbecame 3.0 V. The degree of utilization of the heavy-loading dischargecapacity relative to the initial discharge capacity is shown in Table 6.TABLE 6 high temperature storage characteristics 2 increase of heightcapacity after heavy-loading of the high-temperature characteristicsnon-aqueous electrolyte cell(%) storage(%) (%) example 11 1.5 mol/LiBF₄EC/GBL 0.0 84 80 comp. 1.5 mol/LiPF₆ EC/GBL 6.7 59 75 examp. 7 comp. 1.5mol/LiClO₄ EC/GBL 10.0 35 70 examp. 8 comp 1.5 mol/LiCF₃SO₃ EC/GBL 0.080 46 examp. 9

[0140] As can be seen from Table 6, when the cells in ComparativeExamples 7 and 8 are stored at a high temperature of 60° C., thenon-electrolyte is decomposed to generate gas so that the height of thecell is increased, the contact between the electrode and the electrodecase is worsened, and the internal resistance of the cell is increased.Accordingly, no sufficient discharge capacity can be obtained. InComparative Example 9, the electric conductivity of LiCF₃SO₃ is low sothat the resulting cell is inferior in the desired loading dischargecharacteristics.

[0141] On the other hand, the cell in Example 11 does not generate gasduring storage even at high temperatures, and the internal resistance isnot increased, thus achieving sufficient capacity and excellent heavyloading characteristics.

[0142] D. Experiment for Examining Characteristics on the Concentrationof Supporting Electrolyte in Electrolyte

Reference Example 3

[0143] A cell was prepared in the same manner as in Example 11 exceptthat the concentration of the supporting electrolyte in the non-aqueouselectrolyte was 1.0 mol/l.

Example 14

[0144] A cell was prepared in the same manner as in Example 11 exceptthat the concentration of the supporting electrolyte in the non-aqueouselectrolyte was 1.3 mol/l.

Example 15

[0145] A cell was prepared in the same manner as in Example 11 exceptthat the concentration of the supporting electrolyte in the non-aqueouselectrolyte was 1.8 mol/l.

Reference Example 4

[0146] A cell was prepared in the same manner as in Example 11 exceptthat the concentration of the supporting electrolyte in the non-aqueouselectrolyte was 2.0 mol/l.

[0147] The thus constructed cells in the Examples 11, 14 and 15 andReference Examples 3 and 4 were initially charged for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V, to determinetheir initial discharge capacity, their discharge capacity in alow-temperature atmosphere and heavy loading discharge capacity. Theresults are shown in Table 7. The initial discharge capacity wasmeasured in the same manner as in Experiment A and the capacity in alow-temperature atmosphere was measured in the same manner as in theExperiment B, and the heavy loading discharge capacity was measured inthe same manner as in Experiment C. TABLE 7 low-temperatureheavy-loading characteristics characteristics non-aqueous electrolyte(%) (%) ref. 1.0 mol/LiBF₄ EC/GBL 67 52 examp.3 example 1.3 mol/LiBF₄EC/GBL 75 79 14 example 1.5 mol/LiBF₄ EC/GBL 81 80 11 example 1.8mol/LiBF₄ EC/GBL 77 80 15 ref. 2.0 mol/LiBF₄ EC/GBL 65 78 examp.4

[0148] As can be seen from this table, the rate of transfer of lithiumion in the non-aqueous electrolyte becomes optimum when theconcentration of the supporting electrolyte in the non-aqueouselectrolyte is in the range of 1.3 mol/l to 1.8 mol/l, thus providing acell excellent in low-temperature characteristics and heavy loadingcharacteristics.

[0149] Now, the examples where the material of the cathode case wasexamined are described.

Example 16

[0150] As the cathode case in Example 5 above, there was used a cathodecase produced by plating with nickel the external surface of a stainlesssteel sheet prepared by adding 0.20 part by weight of niobium, 0.20 partby weight of titanium and 0.10 part by weight of aluminum to aferrite-based stainless steel stock containing 28.50 to 32.00% chromiumand 1.50 to 2.50% molybdenum, followed by pressing the nickel-platedstainless steel sheet.

Example 17

[0151] As the cathode case in Example 5 above, there was used a cathodecase produced by plating with nickel the external surface of a stainlesssteel sheet prepared by adding 0.10 part by weight of niobium, 0.10 partby weight of titanium and 0.05 part by weight of aluminum to aferrite-based stainless steel stock containing 28.50 to 32.00% chromiumand 1.50 to 2.50% molybdenum, followed by pressing the nickel-platedstainless steel sheet.

Example 18

[0152] As the cathode case in Example 5 above, there was used a cathodecase produced by plating with nickel the external surface of a stainlesssteel sheet prepared by adding 0.30 part by weight of niobium, 0.30 partby weight of titanium and 0.15 part by weight of aluminum to aferrite-based stainless steel stock containing 28.50 to 32.00% chromiumand 1.50 to 2.50% molybdenum, followed by pressing the nickel-platedstainless steel sheet.

Comparative Example 10

[0153] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 0.05 part by weight of niobium, 0.05 part by weightof titanium and 0.025 part by weight of aluminum to a ferrite-basedstainless steel stock containing 28.50 to 32.00% chromium and 1.50 to2.50% molybdenum, followed by pressing the nickel-plated stainless steelsheet.

Comparative Example 11

[0154] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 0.40 part by weight of niobium, 0.40 part by weightof titanium and 0.20 part by weight of aluminum to a ferrite-basedstainless steel stock containing 28.50 to 32.00% chromium and 1.50 to2.50% molybdenum, followed by pressing the nickel-plated stainless steelsheet.

Comparative Example 12

[0155] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 28.50 to 32.00 parts by weight of chromium and 1.50to 2.50 parts by weight of molybdenum, followed by pressing thenickel-plated stainless steel sheet. This stainless steel is anequivalent product to JIS SUS447J1.

Comparative Example 13

[0156] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 17.00 to 20.00 parts by weight of chromium and 1.75to 2.50 parts by weight of molybdenum to a ferrite-based stainless steelstock, followed by pressing the nickel-plated stainless steel sheet.This stainless steel is an equivalent product to JIS SUS444.

Comparative Example 14

[0157] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel preparedby adding 16.00 to 18.00 parts by weight of chromium and 2.00 to 3.00parts by weight of molybdenum and 10.00˜14.00 parts by weight of nickelto an austenite-based stainless steel stock, followed by pressing thenickel-plated stainless steel sheet. This stainless steel is anequivalent product to JIS SUS316.

[0158] The chemical components in the stainless steel sheets used in theExamples and Comparative Examples above are shown in Table 8. TABLE 8chemical components (wt %) C Si Mn P S Ni Cr Mo N Nb Ti Al example 160.007 0.20 0.20 — — — 30.00 2.00 0.010 0.20 0.20 0.10 example 17 0.0070.20 0.20 — — — 30.00 2.00 0.010 0.10 0.10 0.05 example 18 0.007 0.200.20 — — — 30.00 2.00 0.010 0.30 0.30 0.15 comp.examp.10 0.007 0.20 0.20— — — 30.00 2.00 0.010 0.05 0.05 0.025 comp.examp.11 0.007 0.20 0.20 — —— 30.00 2.00 0.010 0.40 0.40 0.20 comp.examp.12 <0.010 <0.40 <0.40<0.030 <0.020 — 28.50˜32.00 1.50˜2.50 <0.015 — — — JIS SUS447J1comp.examp.13 <0.025 <1.00 <1.00 <0.040 <0.030 — 17.00˜20.00 1.75˜2.50<0.025 — — — JIS SUS444 comp.examp.14 <0.080 <1.00 <2.00 <0.045 <0.03010.00˜14.00 16.00˜18.00 2.00˜3.00 — — — — JIS SUS316

[0159] 1000 cells in each of Examples 16 to 18 and Comparative Examples10 to 14 were constructed and initially charged for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V, and then 50cells in each example were stored at 60° C. under dry conditions for 20days during which a constant voltage of 4.4 V was applied, and thepresence of pits on the cathode case was confirmed under a test glass.The number of pits generated is shown in Table 9. TABLE 9 number ofnumber of the tested the pits cells generated example 16 50 0 example 1750 0 example 18 50 0 comp.examp.10 50 21 comp.examp.11 50 4comp.examp.12 50 23 comp.examp.13 50 50 comp.examp.14 50 50

[0160] As can be seen from Table 9, no pitting occurred in the cells inExamples 16 to 18, but pitting was recognized the cells in ComparativeExample 10 where niobium, titanium and aluminum were added in smalleramounts. Pitting was also recognized in Comparative Examples 12 to 14where niobium, titanium and aluminum were not added. From the foregoing,it is found that in the non-aqueous electrolyte cells at a high voltageof 4 V or more, the pitting potential of the stainless steel stock towhich chromium and molybdenum were added is lower than the potential ofthe cathode active material, thus causing the material in the cathodemember to be eluted into the electrolyte to generate pits. Even ifniobium, titanium and aluminum are added in smaller amounts, pittingoccurs.

[0161] It was found that even in Comparative Example 11 wherein niobium,titanium and aluminum were added in larger amounts, a few pits weregenerated. This is probably because addition of titanium and aluminum inlarger amounts causes inclusions and precipitates to be separated andformed, resulting in deterioration in resistance to pitting.

[0162] In these examples, an electricity-generating element comprisingthe cathode and anode wound via the separator was used. However, thesame effect could be achieved even by use of an electricity-generatingelement comprising cathodes and anodes laminated via a separator or anelectricity generating element comprising a cathode and an anode bentalternately via a separator.

Example 19

[0163] As the cathode case in Example 5 above, there was used a cathodecase produced by plating with nickel the external surface of a stainlesssteel sheet prepared by adding 0.85 part by weight of niobium, 0.1 partby weight of titanium and 0.25 part by weight of copper to ferrite-basedstainless steel containing 20.00 to 23.00% chromium and 1.50 to 2.50%molybdenum, followed by pressing the nickel-plated stainless steel.

Example 20

[0164] As the cathode case in Example 5 above, there was used a cathodecase produced by plating with nickel the external surface of a stainlesssteel sheet prepared by adding 0.80 part by weight of niobium, 0.05 partby weight of titanium and 0.20 part by weight of copper to aferrite-based stainless steel stock containing 20.00 to 23.00% chromiumand 1.50 to 2.50% molybdenum, followed by pressing the nickel-platedstainless steel sheet.

Example 21

[0165] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 0.90 part by weight of niobium, 0.15 part by weightof titanium and 0.30 part by weight of copper to a ferrite-basedstainless steel stock containing 20.00 to 23.00% chromium and 1.50 to2.50% molybdenum, followed by pressing the nickel-plated stainless steelsheet.

Comparative Example 15

[0166] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 0.75 part by weight of niobium, 0.03 part by weightof titanium and 0.15 part by weight of copper to a ferrite-basedstainless steel stock containing 20.00 to 23.00% chromium and 1.50 to2.50% molybdenum, followed by pressing the nickel-plated stainless steelsheet.

Comparative Example 16

[0167] As the cathode case, there was used a cathode case produced byplating with nickel the external surface of a stainless steel sheetprepared by adding 0.95 part by weight of niobium, 0.20 part by weightof titanium and 0.35 part by weight of copper to a ferrite-basedstainless steel stock containing 20.00 to 23.00% chromium and 1.50 to2.50% molybdenum, followed by pressing the nickel-plated stainless steelsheet.

[0168] The chemical components in the stainless steel sheets used inExamples 19 to 21 and Comparative Examples 13 to 16 are shown in Table10. TABLE 10 chemical components(wt %) C Si Mn P S Ni Cr Mo N Nb Ti Cuexample 19 0.007 0.15 0.10 — — 0.2 22.00 2.00 — 0.85 0.10 0.25 example20 0.007 0.15 0.10 — — 0.2 22.00 2.00 — 0.80 0.05 0.20 example 21 0.0070.15 0.10 — — 0.2 22.00 2.00 — 0.90 0.15 0.30 comp.examp.15 0.007 0.150.10 — — 0.2 22.00 2.00 — 0.75 0.03 0.15 comp.examp.16 0.007 0.15 0.10 —— 0.2 22.00 2.00 — 0.95 0.20 0.35 comp.examp.13 <0.025 <1.00 <1.00<0.040 <0.030 — 17.00˜20.00 1.75˜2.50 <0.025 — — — JIS SUS444comp.examp.14 <0.080 <1.00 <2.00 <0.045 <0.030 10.00˜14.00 16.00˜18.002.00˜3.00 — — — — JIS SUS316

[0169] 1000 cells in each of Examples 19 to 21 and Comparative Examples13 to 16 were constructed and initially charged for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V, and then 50cells in each example were stored at room temperature for 6 monthsduring which a constant voltage of 4.4 V was applied, and the presenceof pits on the cathode case was examined under a test glass. Inaddition, 200 cells in each example were stored for 100 days in anatmosphere at 45° C. under 93% humidity, and electrolyte leakage wasexamined under a test glass. Number of cells wherein pitting andelectrolyte leakage occurred is shown in Table 11. TABLE 11 result ofpitting test number of result of leakage test number of the cells numberof number of the tested pits the tested the liquid-leaked cellsgenerated cells cells example 19 50 0 200 0 example 20 50 0 200 0example 21 50 0 200 0 comp.examp.15 50 3 200 0 comp.examp.16 50 6 200 2comp.examp.13 50 50 200 1 comp.examp.14 50 50 200 0

[0170] As can be seen from Table 11, no pitting occurred in the cells inExamples 19˜21. However, pitting was observed in Comparative Example 15wherein niobium, titanium and copper were added in smaller amounts. Onthe other hand, pitting and electrolyte leakage were recognized inComparative Example 16 wherein niobium, titanium and copper were addedin larger amounts. In Comparative Examples 13 and 14 wherein chromiumand molybdenum were added, pitting was recognized, and particularly inComparative Example 13, electrolyte leakage was also recognized.

[0171] From the foregoing, it is found that in the non-aqueouselectrolyte cells at a high voltage of 4 V or more, the pittingpotential of the stainless steel stock to which chromium and molybdenumwere added is lower than the potential of the cathode active material,thus causing the material in the cathode member to be eluted into theelectrolyte to generate pits, but by adding niobium, titanium andcopper, the pitting potential of the stainless steel stock is madehigher than the potential of the cathode active material, thuspreventing pitting.

[0172] However, if niobium, titanium and copper are added in smalleramounts, the pitting potential of the stainless steel is not enough forthe potential of the cathode active material, thus causing pitting. Onthe other hand, if niobium, titanium and copper are added in largeramounts, inclusions and precipitates of additives contained in thestainless steel stock are easily separated and formed thus deterioratingresistance to pitting, and further by the influence of niobium,formation of ferrite is promoted to make the steel stock rigid andhardly processed.

[0173] In these examples, an electricity-generating element comprisingthe cathode and anode wound via the separator was used. However, thesame effect could be achieved even by use of an electricity-generatingelement comprising cathodes and anodes laminated via a separator or anelectricity generating element comprising a cathode and an anode bentalternately via a separator.

[0174] Now, the examples wherein a metal net is provided between thecathode or anode cases and the electrode group in the present inventionare described.

Example 22

[0175] A sectional drawing of the cell in this example is shown in FIG.6. In the same cell as in Example 5, a stainless steel metal net 6 of0.03 mm in thickness was welded into the internal surfaces of thecathode and anode cases. The other procedure was the same as in Example5. The total thickness of the cathode and anode cases and the metal netwas 0.28 mm.

Example 23

[0176] A cell was prepared in the same manner as in Example 22 exceptthat a metal net of 0.05 mm in thickness was welded into the internalsurfaces of the cathode and anode cases, and the total thickness of thecathode and anode cases and the metal net was 0.30 mm.

Example 24

[0177] A cell was prepared in the same manner as in Example 22 exceptthat a metal net of 0.10 mm in thickness was welded into the internalsurfaces of the cathode and anode cases, and the total thickness of thecathode and anode cases and the metal net was 0.35 mm.

Example 25

[0178] A cell was prepared in the same manner as in Example 22 exceptthat a metal net of 0.15 mm in thickness was welded into the internalsurfaces of the cathode and anode cases, and the total thickness of thecathode and anode cases and the metal net was 0.40 mm.

Example 26

[0179] A cell was prepared in the same manner as in Example 22 exceptthat a metal net of 0.20 mm in thickness was welded into the internalsurfaces of the cathode and anode cases, and the total thickness of thecathode and anode cases and the metal net was 0.45 mm.

Example 27

[0180] A cell was prepared in the same manner as in Example 22 exceptthat a metal net of 0.30 mm in thickness was welded into the internalsurfaces of the cathode and anode cases, and the total thickness of thecathode and anode cases and the metal net was 0.55 mm.

Comparative Example 17

[0181] A cell was prepared in the same manner as in Example 22 exceptthat the metal net was not used, and the cathode and anode cases havinga conductive coating applied onto the internal surface of a cell case of0.25 mm in thickness were used.

[0182] A stainless steel lead terminal of 0.2 mm in thickness wasresistance-welded at a welding power of 480±10V into each of cathode andanode cases in 300 cells thus constructed in the Examples andComparative Examples. Fifty cells were picked up at random, dismantled,and examined for generation of holes and shrinkage in the separator atthe sides of the cathode and anode, and the degree of removal of theelectrodes. In addition, these cells were initially charged for 48 hoursat a constant current of 3 mA at a constant voltage of 4.2 V, then leftfor 3 days at room temperature, and measured for the voltage in the opencircuit. Thereafter, the cells in which the voltage in the open circuitafter 3 days was 4.0 V or more were discharged at a constant current of1 mA until 3.0 V, to determine their discharge capacity.

[0183] The generation of holes and shrinkage in the separator at thesides of the cathode and anode, and the degree of removal of theelectrodes are shown in Table 12. Further, the number of the cells whosevoltage was less than 4.0 V in the open circuit after the cells wereleft for 3 days after initial charge, as well as the mean dischargecapacity of the cells 3 days later wherein the voltage in the opencircuit was 4.0 V or more, is shown in Table 13.

[0184] As is evident from the table, the cells of this invention in theExamples, as compared with the cell in Comparative Example 17, attainsignificant improvements against the generation of holes and shrinkagein the separator at the sides of the cathode and anode, and the removalof the electrodes, after the lead wire was resistance-welded into thecell, and the short-circuiting of the cells was also improved. In theExamples wherein the total thickness of the cathode and anode cases andthe metal net was 0.30 mm or more, generation of holes and shrinkage inthe separator at the sides of the cathode and anode, and removal of theelectrodes are hardly observed after the lead terminal wasresistance-welded into the cell. The cell in Example 22 showed slightshrinkage of the separator at the sides of the cathode and anode afterresistance welding, but no short-circuiting occurred in the cell. In thecells in Examples 23, 24, 25 and 26, the thickness of the metal net isoptimum so that a lot of electrodes can be packed in cells to givehigh-capacity cells. Accordingly, the total of the thickness of each ofthe cathode and anode cases and the thickness of the metal net is morepreferably 0.30 mm to 0.45 mm. TABLE 12 the ratio of accidentalgeneration in the total thickness separator or the electrode of the casegeneration of and the holes in the shrinkage in removal in metal net(mm) separator the separator the electrodes comp. no net 50/50 50/5050/50 examp.17 0.25 example 0.28  0/50  2/50  0/50 22 example 0.30  0/50 0/50  0/50 23 example 0.35  0/50  0/50  0/50 24 example 0.40  0/50 0/50  0/50 25 example 0.45  0/50  0/50  0/50 26 example 0.55  0/50 0/50  0/50 27

[0185] TABLE 13 number of the cells having the voltage in totalthickness of the open curcuit less discharge the case and the than 4.0 V3 days capacity metal net (mm) after initial charge (mAh) comp. no net50/50 18 examp.17 0.25 example 22 0.28 0/50 73 example 23 0.30 0/50 73example 24 0.35 0/50 71 example 25 0.40 0/50 69 example 26 0.45 0/50 67example 27 0.55 0/50 63

[0186] Now, the examples wherein a non-metallic thermal insulator isprovided between the cathode or anode case and the separator in thepresent invention are described.

Example 28

[0187] Sectional drawings of the cell in this example are shown in FIGS.7 and 8. As shown in these drawings, the same electrode group as inExample 5 above was constructed, and a part of 100 mm from the edge andon one side of the electrode was used as an electrically connectingpart. Hence, the anode active material-containing layer 4 b was removed,and further the anode active material-containing layer 4 b on a regionof 22 mm from the edge of the back of said electrode was removed toprovide an anode plate 4. As shown in the drawings, a glass tape of 0.03mm in thickness was attached as thermal insulator 16 onto the region of22 mm from which the anode active material-containing layer on the anodeplate 4 had been removed. This glass tape was prepared by coating oneside of a glass cloth of 11 mm in length and 16 mm in width as thesubstrate with an adhesive material. The thermal insulator 16 wasattached also on a cathode plate 2 in the same manner. The sameprocedure as in Example 5 was conducted except for the above procedure.In these drawings, 2 indicates a cathode plate, 2 a indicates a cathodecurrent collecting body, 2 b indicates a cathode active materialcontaining layer and 4 a indicates an anode current collecting body.

Example 29

[0188] A cell was constructed in the same manner as in Example 28 exceptthat a glass tape of 0.05 mm in thickness was attached to each of thecathode and anode plates.

Example 30

[0189] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.14 mm, and a glass tape of 0.10 mm inthickness was attached to each of the cathode and anode plates.

Example 31

[0190] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.13 mm, and a glass tape of 0.15 mm inthickness was attached to each of the cathode and anode plates.

Example 32

[0191] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.12 mm, and a glass tape of 0.20 mm inthickness was attached to each of the cathode and anode plates.

Example 33

[0192] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.10 mm, and a glass tape of 0.30 mm inthickness was attached to each of the cathode and anode plates.

Example 34

[0193] A cell was constructed in the same manner as in Example 28 exceptthat a PTFE tape prepared by coating one side of a PTFE tape of 0.03 mmin thickness with an adhesive was attached to each of the cathode andanode plates.

Example 35

[0194] A cell was constructed in the same manner as in Example 28 exceptthat a PTFE tape of 0.05 mm in thickness was attached to each of thecathode and anode plates.

Example 36

[0195] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.14 mm, and a PTFE tape of 0.10 mm inthickness was attached to each of the cathode and anode plates.

Example 37

[0196] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.13 mm, and a PTFE tape of 0.15 mm inthickness was attached to each of the cathode and anode plates.

Example 38

[0197] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.12 mm, and a PTFE tape of 0.20 mm inthickness was attached to each of the cathode and anode plates.

Example 39

[0198] A cell was constructed in the same manner as in Example 28 exceptthat the thickness of the active material-containing layer on each ofthe cathode and anode was 0.10 mm, and a PTFE tape of 0.30 mm inthickness was attached to each of the cathode and anode plates.

Comparative Example 18

[0199] A cell was constructed in the same manner as in Example 28 exceptthat no thermal insulator was attached to the cathode and anode plates.

[0200] A stainless steel lead terminal of 0.2 mm in thickness was weldedby resistance welding at an output voltage of 480±10 V into each of thecathode and anode cell cases in 300 cells thus constructed in each ofthe Examples and Comparative Examples. Fifty cells were picked up atrandom, dismantled, and examined for generation of holes and shrinkagein the separator at the sides of the cathode and anode, and the degreeof removal of the electrodes. Fifty cells in each example were picked upat random from the remaining cells, charged initially for 48 hours at aconstant current of 3 mA at a constant voltage of 4.2 V, left for 3 daysat room temperature, and measured for the voltage in the open circuit.Thereafter, the cells in which said voltage in the open circuit was 4.0V or more were selected and discharged at a constant current of 1 mAuntil 3.0 V, to determine their discharge capacity.

[0201] The generation of holes and shrinkage in the separator, and thedegree of removal of the electrodes in the cells in the Examples andComparative Examples, the number of cells wherein the voltage in theopen circuit was less than 4.0 V after left for 3 days, and the meandischarge voltage thereafter, are shown in Table 14. TABLE 14 the ratioof accidental generation in the separator or the electrode number of thecells material thickness generation having the voltage in of of thermalof holes shrinkage removal the open circuit less discharge thermalinsulator in the in the in the than 4.0 V 3 days after capacityinsulator (mm) separator separator electrodes initial charge (mAh) comp.— none 50/50  50/50  50/50  50 — examp.18 example glass 0.01 0/50 2/502/50 3 67 28 tape example 0.05 0/50 0/50 1/50 0 67 29 example 0.10 0/500/50 0/50 0 65 30 example 0.15 0/50 0/50 0/50 0 63 31 example 0.20 0/500/50 0/50 0 61 32 example 0.30 0/50 0/50 0/50 0 57 33 example PTFE 0.010/50 2/50 4/50 3 67 34 example 0.05 0/50 0/50 1/50 0 67 35 example 0.100/50 0/50 0/50 0 65 36 example 0.15 0/50 0/50 0/50 0 63 37 example 0.200/50 0/50 0/50 0 61 38 example 0.30 0/50 0/50 0/50 0 57 39

[0202] Examples, as compared with the cell in Comparative Example 18,attain significant improvements against the generation of holes andshrinkage in the separator at the sides of the cathode and anode, andthe removal of the electrodes, after the lead wire was resistance-weldedinto the cell, and further the short-circuiting in the cells wasinhibited, and the number of the cells showing a reduction in thevoltage in the open circuit was decreased. In Examples 29 to 33 andExamples 35 to 39 wherein the thickness of the thermal insulator, thatis, a glass tape or a PTFE tape of fluorine resin, is 0.05 mm or more,generation of holes and shrinkage in the separator at the sides of thecathode and anode, removal of the electrodes and a reduction in thevoltage in the open circuit are hardly observed after the lead terminalwas resistance-welded into the cell. In the cells in Examples 29 to 32and Examples 35 to 38, the thickness of the thermal insulator is optimumso that a lot of active materials can be packed in cells to givehigh-capacity cells.

[0203] In the Examples of the invention, the cells wherein glass or PTFEwas used as the substrate material for the non-metal thermal insulator,but the same effect can be achieved even when FEP, ETFE, PFA, PVDF,polyimide, LCP, PPS, or PBT was used as the substrate material. Further,the flat non-aqueous solvent secondary cells wherein a non-aqueoussolvent was used as the non-aqueous electrolyte has been described inthe Examples of this invention, but these examples can be applied topolymer secondary cells using a polymer electrolyte as the non-aqueouselectrolyte or solid electrolyte secondary cells using a solidelectrolyte. Further, these examples are useful for cells wherein apolymer thin film or solid electrolyte film damaged easily by heatduring welding has been used in place of the resin separator. The cellsdescribed above are mainly coin-shaped wherein the opening was sealed bycaulking the cathode case, but the cathode and anode may be exchanged sothat the opening of the anode case is sealed by caulking. Further, theshape of the cell may not be necessarily round, and the presentinvention can also be applied to flat non-aqueous electrolyte secondarycells of unique elliptic or rectangular shape.

[0204] Now, the examples where a cutting is provided in the cathode casein the present invention are described

Example 40

[0205] A sectional drawing of the cell in this example is shown in FIG.9, and its cathode case is shown in FIG. 10.

[0206] A flat non-aqueous electrolyte secondary cell was prepared in thesame manner as in Example 5 except that the cathode case 1 had a heightof 3 cm and a diameter of 24.5 mm, and as shown in FIGS. 9 and 10, thecathode case was provided with the cut part 1 a, and the dimension ofthe cut part 1 a had a width of 0.1 grad in terms of its central angleto the circumference of the cathode case and a depth of 0.15 mm indepth. Further, the cathode case was sealed by caulking in thedirections of diameter and height.

Example 41

[0207] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.1 πrad and a depth of 0.90 mm in depth.

Example 42

[0208] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.9 πrad and a depth of 0.15 mm in depth.

Example 43

[0209] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.9 πrad and a depth of 0.90 mm in depth.

Comparative Example 19

[0210] A cell was prepared in the same manner as in Example 40 exceptthat no cutting was provided in the cathode case 1.

Comparative Example 20

[0211] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.1 πrad and a depth of 0.10 mm in depth.

Comparative Example 21

[0212] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.1 πrad and a depth of 0.95 mm in depth.

Comparative Example 22

[0213] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.05 πrad and a depth of 0.90 mm in depth.

Comparative Example 23

[0214] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.95 πrad and a depth of 0.15 mm in depth.

Comparative Example 24

[0215] A cell was prepared in the same manner as in Example 40 exceptthat the cut part 1 a provided in the cathode case 1 had a central angleof 0.1 πrad and a depth of 0.15 mm in depth, and the cathode case 1 wassealed by caulking in only the direction of diameter.

[0216] Fifty cells thus constructed in each example were initiallycharged for 48 hours at a constant current of 3 mA at a constant voltageof 4.2 V, and then stored for 100 days at 45° C. under 93% relativehumidity, and the number of cells with electrolyte leakage wasdetermined. Further, the cells were examined in a test where they wereforcibly discharged at a constant current of 300 mAh for 6 hours, or ina test where they were heated at 160° C. for 10 minutes after heated atan increasing temperature of 5° C./min., and the number of broken cellswas examined.

[0217] The test results are shown in Table 15. Electrolyte leakage didnot occur during storage in the cells in the Examples and ComparativeExamples 19, 20 and 22. On the other hand, in Comparative Example 21,the electrolyte was leaked through the cutting, because the cut part wastoo deep. Further, in Comparative Example 23, the width of the cuttingwas too broad, and thus in Comparative Example 24, the degree ofcompression of the insulating gasket could not be increased, thusdeteriorating air-tightness to permit electrolyte leakage.

[0218] In the forcible discharge test and the heating test, the cells inthe Examples and Comparative Examples 21, 23 and 24 were not broken,while the cells in Comparative Examples 19, 20 and 22 were brokenbecause the cathode case could not be deformed, thus failing to open theinsulating gasket. TABLE 15 number of broken cells number of at the sizeof a cutting cells with forcibly at the width depth electrolytedischarge heating (rad) (mm) leakage test test example 40 0.1 π 0.150/30 0/10 0/10 example 41 0.1 π 0.90 0/30 0/10 0/10 example 42 0.9 π0.15 0/30 0/10 0/10 example 43 0.9 π 0.90 0/30 0/10 0/10 comp. nocutting 0/30 0/10 0/10 examp.19 comp. 0.1 π 0.10 0/30 0/10 0/10 examp.20comp. 0.1 π 0.95 24/30  0/10 0/10 examp.21 comp. 0.05 π  0.90 0/30 0/100/10 examp.22 comp. 0.95 π  0.15 19/30  0/10 0/10 examp.23 comp. 0.1 π0.15 29/30  0/10 0/10 examp.24

[0219] As described above, the cutting in the cathode case is formedsuch that its width is 0.1 π to 0.9 πrad in terms of its central anglerelative to the circumference of the cathode case and simultaneously itsdepth is 5 to 30% of the height of the cathode case, whereby a flatnon-aqueous electrolyte secondary cell free of breakage under abnormalconditions and free of electrolyte leakage during storage can beprovided.

[0220] In the above examples, the flat non-aqueous solvent secondarycells wherein a non-aqueous solvent was used as the non-aqueouselectrolyte, but the same effect can also be achieved by a polymersecondary cell using a polymer electrolyte as the non-aqueouselectrolyte or by a solid electrolyte secondary cell using a solidelectrolyte. Further, a polymer thin film or a solid electrolyte filmcan also be used in place of the resin separator. The cell having asingle cutting was described above, but the cell having a plurality ofcuttings can also achieve the same effect if the width of cuttings intotal has a central angle of 0.1 π to 0.9 πrad relative to thecircumference of the cathode case. The cells described above are mainlycoin-shaped electrolyte cells wherein the opening was sealed by caulkingthe cathode case, but the cathode and anode may be exchanged so that theanode case is provided with the cutting, and the opening of the anodecase may be sealed by caulking.

[0221] Now, examples of flat non-aqueous electrolyte secondary cellswherein one or two grooves are formed on the sealed-opening portion R inthe cathode case in the lengthwise direction to form a thin-plate partare described.

Example 44

[0222] This example is described by reference to FIGS. 11, 12 and 13.FIG. 11 is a sectional drawing of the cell in this example; FIG. 12shows the opening-sealed portion R in the cathode case in FIG. 11; andFIG. 13 is a sectional drawing of the cathode case 1.

[0223] In the cathode case 1, the opening-sealed portion R is providedwith one groove thin plate portion 1 b. The cells were provided with oneof 7 types of groove thin plate portion 1 b having a thickness rangingby 0.02 mm from 0.05 mm to 0.17 mm. Ten cells provided with each type ofportion 1 b were initially charged for 48 hours at a constant current of3 mA at a constant voltage of 4.2 V, and then examined in a test wherethey were forcibly discharged at a constant current of 300 mA for 6hours, or in a test where they were heated at 160° C. for 10 minutesafter heated at an increasing temperature of 5° C./min., and then thenumber of broken cells was examined. Further, 30 cells provided witheach type of portion 1 b were stored for 100 days at 45° C. under 93%relative humidity, and electrolyte leakage was examined.

Example 45

[0224] The secondary cell in Example 44 was provided with two portions 1b in the cathode vessel and then evaluated in the same manner as above.

[0225] The test results are shown in Table 16. When the thickness ofportion 1 b was 0.17 mm, the cells were broken to scatter the cellcontent without rupture of one or two portions lb. When the thickness ofportion 1 b was 0.05 mm, electrolyte leakage occurred through one or twoportions 1 b, because the portion 1 b was too thin thus causing ruptureupon sealing of the opening, to deteriorate sealability of the opening.TABLE 16 the cathode case example 44 example 45 thickness one thin plateportion two thin plate portion of at the number of at the number of thinplate forcibly at the cells with forcibly at the cells with portiondischarge heating electrolyte discharge heating electrolyte (mm) testtest leakage test test leakage 0.05 0/10 0/10 3/30 0/10 0/10 5/30 0.070/10 0/10 0/30 0/10 0/10 0/30 0.09 0/10 0/10 0/30 0/10 0/10 0/30 0.110/10 0/10 0/30 0/10 0/10 0/30 0.13 0/10 0/10 0/30 0/10 0/10 0/30 0.150/10 0/10 0/30 0/10 0/10 0/30 0.17 3/10 1/10 0/30 2/10 2/10 0/30

[0226] As can be seen from these results, the flat non-aqueous solventsecondary cell free of breakage and leakage can be obtained by allowingthe thickness of the thin plate portion 1 b to be in the range of 0.07to 0.15 mm.

[0227] In Examples 44 and 45 in the present invention, the flatnon-aqueous solvent secondary cells using a non-aqueous solvent as thenon-aqueous electrolyte were described, but the same effect can beachieved by a polymer secondary cell using a polymer electrolyte as thenon-aqueous electrolyte or by a solid electrolyte secondary cell using asolid electrolyte.

[0228] Now, the examples where a shattering groove having a concaveshape in section is formed on the external surface of the anode case inthe present invention are described.

Example 46

[0229] The anode case 5 in the cell in Example 5 above was provided withthe shattering groove 5 e having a concave shape in section, as shown inFIGS. 14 and 15. This shattering groove 5 e is branched at the terminalsthereof. FIG. 14 is a sectional drawing of the cell in this example, andFIG. 15 is a top view of the anode case in FIG. 14.

Example 47

[0230] In this example, the shape of the shattering groove is differentfrom that of Example 46, and as shown in FIG. 16 (top view of the anodecase), the shattering groove 5 f having a concave shape in section has ahalf-round shape along the circumference in the bottom of the anode case5.

Example 48

[0231] As shown in FIG. 17 (top view of the anode case), the shatteringgroove 5 g having a concave shape in section has a ¼ circular shapealong the circumference in the bottom of the anode case 5, and twoshattering grooves 5 g face each other.

Example 49

[0232] In the shattering groove 5 h having a concave shape in section asshown in FIG. 18 (top view of the anode case), a half-round shatteringgroove along the circumference in the bottom of the anode case 5 isconnected in T form to one shattering groove.

Example 50

[0233] As shown in FIG. 19 (top view of the anode case), the shatteringgroove 5 i having a concave shape in section is linear.

Example 51

[0234] As shown in FIG. 20 (top view of the anode case), the shatteringgroove 5 j having a concave shape in section has a shape such as 3 linesgathered at central.

Example 52

[0235] As shown in FIG. 21 (top view of the anode case), the shatteringgroove 5 k having a concave shape in section has a shape such as 5 linesgathered at central.

Comparative Example 25

[0236] As shown in FIG. 22 (top view of the anode case), the cathodecase 5 having no shattering groove was used.

Comparative Example 26

[0237] The cell in this example was the same as in Comparative Example25 except that the cathode case 1 was provided with a shattering groovehaving the same shape as that of the shattering groove in Example 46.

Reference Example 5

[0238] A shattering groove having the same shape as in Example 46 isformed not on the external face of the anode case but on the internalface of the anode case.

[0239] Fifty cells in each group were initially charged for 48 hours ata constant current of 3 mA at a constant voltage of 4.2 V, and thenstored for 100 days at 60° C. under 93% relative humidity, and thenumber of cells with electrolyte leakage was determined. Further, thecells were examined in a test where they were forcibly discharged at aconstant current of 300 mAh for 6 hours, or in a test where they wereheated at 160° C. for 10 minutes after heated at an increasingtemperature of 5° C./min., and then the number of broken cells wasdetermined. The test results are shown in Table 17. TABLE 17 at theforcibly discharge test at the heating test number of period number ofperiod the untill the untill number of effectly shattering numbereffectly shattering cells with number worked groove of worked grooveelectrolyte of broken shattering worked broken shattering worked leakagecells groove (hrs.) cells groove (min.) example 46 0/30 0/10 10/10  5˜5.5 0/10 10/10 25˜32 example 47 0/30 0/10 10/10   5˜5.5 0/10 10/1026˜33 example 48 0/30 0/10 10/10 5.2˜5.7 0/10 10/10 31˜36 example 490/30 0/10 10/10 4.8˜5.3 0/10 10/10 21˜24 example 50 0/30 0/10 10/105.2˜5.6 0/10 10/10 26˜33 example 51 0/30 0/10 10/10 5.2˜5.5 0/10 10/1030˜36 example 52 0/30 0/10 10/10 5.0˜5.4 0/10 10/10 29˜34 comp. 0/3010/10  10/10 — 10/10  — — examp.25 comp. 21/30  0/10 10/10   5˜5.5 0/1010/10 25˜32 examp.26 ref. 0/30 0/10 10/10 5.3˜5.9 1/10  9/10 31˜37examp.5

[0240] As can be seen from Table 17, no electrolyte leakage occurredduring storage in the cells in Comparative Example 25 and ReferenceExample 5. On the other hand, in Comparative Example 26, the cathodecase was corroded during storage, and the electrolyte was leaked througha part of the shattering groove. Further, in Reference Example 5, onetenth of the cells were broken in the heating test. This is probablybecause the actuation of the shattering groove in the cell was delayed.

[0241] As shown in Table 17, a flat non-aqueous electrolyte secondarycell free of breakage under abnormal conditions and free of electrolyteleakage during storage can be obtained by providing it with one or moreshattering grooves having a concave shape in section.

[0242] In the above examples, the flat non-aqueous electrolyte secondarycells using a non-aqueous solvent in the non-aqueous electrolyte weredescribed, but the same effect can be achieved by a polymer secondarycell using a polymer electrolyte as the non-aqueous electrolyte or by asolid electrolyte secondary cell using a solid electrolyte. Further, apolymer thin film or a solid electrolyte film can also be used in placeof the resin separator.

[0243] Now, the examples where unevenness or protrusions are provided inthe inside of the cathode and anode cases in the present invention aredescribed.

Example 53

[0244] A sectional drawing and a top view of the cell in this exampleare shown in FIGS. 23 and 24, respectively.

[0245] In the cell in Example 5, the anode case 5 is provided at thecenter thereof with a protrusion 5 a of 1.0 mm in diameter and 0.2 mm inheight in the direction of from the external to internal surfaces of thevessel. Fifty flat non-aqueous electrolyte secondary cells of 3 mm inthickness and 24.5 mm in diameter in Example 53 were constructed.

Example 54

[0246] Fifty cells were constructed in the same manner as in Example 53except that the anode case was not provided with any protrusion, and thecathode case was provided at the center thereof with a protrusion 5 a of1.0 mm in diameter and 0.2 mm in height in the direction of from theexternal to internal surfaces of the vessel.

Example 55

[0247] Fifty cells were constructed in the same manner as in Example 53except that the cathode cases were provided at the center thereof with aprotrusion 5 a of 1.0 mm in diameter and 0.2 mm in height in thedirection of from the external to internal surfaces of the vessel.

Comparative Example 27

[0248] Fifty cells were constructed in the same manner as in Example 53except that the protrusion-free anode case was used.

[0249] These cells were initially charged for 48 hours at a constantcurrent of 3 mA at a constant voltage of 4.2 V Thereafter, the cellswere discharged at a constant current of 30 mA until 3.0 V, to determinetheir initial discharge capacity. The test results are shown in Table18. Further more, they were discharged at a constant current of 240 mAuntil 3.0V, to determine their heavy-loading discharge capacity. Then,utilization of heavy-loading discharge capacity to initial dischargecapacity are shown in Table 18. TABLE 18 utilization of heavy-loadingprotrusion in protrusion in discharge capacity anode case cathode case(%) example 53 exist none 65 example 54 none exist 65 example 55 existexist 70 comp. none none 52 examp.27

[0250] As is evident from this table, the cells in the ComparativeExamples are inferior in discharge capacity to the cells in theExamples. This is because the electrodes are shrunk upon discharge sothat the contact between the electrode group and the cell vessel isunstabilized to increase the internal resistance. By providingprotrusions as shown in this example, the contact is secured and thussuch a reduction in capacity does not occur.

[0251] Now, the example where the electrode group formed by bendingalternately a cathode sheet and an anode sheet setting each other in aright angled position was used are described.

Example 56

[0252] Sectional drawings of the cell in this example are shown in FIGS.25 and 26. As shown in these drawings, a cathode 2 in sheet shape isstuck with a separator 3 in lager sheet shape than a cathode 2 exceptfor a part contacting at inner face of cathode case 1. An anode 4 insheep shape was set on the above sheet cathode 2 in a right angledposition each other. Thereafter, they were bent alternately to obtainneeded capacity to form the electrode group. This electrode group wereset in a cathode case via a gasket 6, an anode case 5 was set on theabove electrode, then a cathode and anode cases were clipped bycaulking. As shown these drawings, the thickness of the sheet cathodeand anode was about half as their another portions.

[0253] In this example the electric capacity was increased by about 5%than that of the cells shown in FIG. 1 and FIG. 2. This is because theelectrode group in this example is more effectively utilized than thosecells in FIG. 1 and FIG. 2.

1. A flat non-aqueous electrolyte secondary cell comprising a metallicanode case also serving as an anode terminal and a metallic cathode casealso serving as a cathode terminal fit to each other via an insulatinggasket, the anode or cathode case having an opening-sealed structurecaulked by caulking and having in the inside thereof anelectricity-generating element including at least a cathode, a separatorand an anode and a non-aqueous electrolyte, wherein a plurality ofelectrode units each consisting of the cathode and the anode opposite toeach other via the separator are laminated to form an electrode group,and the total sum of the areas of the opposing cathode and anode in thiselectrode group is larger than the area of the opening of saidinsulating gasket.
 2. The flat non-aqueous electrolyte secondary cellaccording to claim 1, wherein at least 3 electrode units are laminatedto form an electrode group.
 3. The flat non-aqueous electrolytesecondary cell according to claim 1, wherein the cathode comprises acathode plate having a cathode active material layer formed on one orboth sides of a cathode current-collecting body, while the anodecomprises an anode plate having an anode active material layer formed onone or both sides of an anode current-collecting body, and the thicknessof the active material layer coated on one side of each of the cathodeand anode current-collecting bodies is 0.03 mm to 0.40 mm.
 4. The flatnon-aqueous electrolyte secondary cell according to claim 1, wherein thecathode comprises a cathode plate having a cathode active material layerformed on one or both sides of a cathode current-collecting body, theanode comprises an anode plate having an anode active material layerformed on one or both sides of an anode current-collecting body, oneterminal of each of the cathode and anode plates forms an electricallyconnecting part by exposing each current-collecting body, theelectrically connecting portions of a plurality of cathode plates areexposed through the separator at the same side so as to be electricallyconnected to the cathode case, while the electrically connectingportions of a plurality of anode plates are exposed through theseparator at the other side to said cathode plates, so as to beelectrically connected to the anode case.
 5. The flat non-aqueouselectrolyte secondary cell according to claim 1, wherein a carbonmaterial having a developed graphite structure wherein the distance offace d₀₀₂ is 0.338 nm or less is used as the anode, and a solutioncomprising lithium borofluoride as a supporting electrolyte dissolved inethylene carbonate and γ-butyrolactone as major solvent is used as thenon-aqueous electrolyte.
 6. The flat non-aqueous electrolyte secondarycell according to claim 1, wherein the ratio by volume of ethylenecarbonate to γ-butyrolactone is from 0.3 to 1.0.
 7. The flat non-aqueouselectrolyte secondary cell according to claim 1, wherein theconcentration of the supporting electrolyte in the non-aqueouselectrolyte is 1.3 to 1.8 mol/l.
 8. The flat non-aqueous electrolytesecondary cell according to claim 1, wherein stainless steel prepared byadding 0.1 to 0.3% niobium, 0.1 to 0.3% titanium and 0.05 to 0.15%aluminum to ferrite-based stainless steel containing 28.50 to 32.00%chromium and 1.50 to 2.50% molybdenum is used as the cathode case alsoserving as a cathode terminal, or as a constituent member for a metallicpart brought directly into contact with the cathode active material. 9.The flat non-aqueous electrolyte secondary cell according to claim 1,wherein stainless steel prepared by adding 0.8 to 0.9% niobium, 0.05 to0.15% titanium and 0.20 to 0.30% copper to ferrite-based stainless steelcontaining 20.00 to 23.00% chromium and 1.50 to 2.50% molybdenum is usedas the cathode case also serving as a cathode terminal, or as aconstituent member for a metallic part brought directly into contactwith the cathode active material.
 10. The flat non-aqueous electrolytesecondary cell according to claim 1, wherein a metal net is providedbetween the cathode case and/or the anode case and the electrode group.11. The flat non-aqueous electrolyte secondary cell according to claim1, wherein a non-metal thermal insulator is provided between the cathodecase and/or the anode case and the separator.
 12. The flat non-aqueouselectrolyte secondary cell according to claim 1, wherein the opening ofthe insulating gasket is sealed through caulking by compressing saidcathode case in the directions of diameter and height, a cutting isprovided in the side of the cathode case, and the width of the cuttingis 0.1 π to 0.9 πrad in terms of central angle to the circumference ofthe cathode case, and the depth of the cutting is 5 to 30% of the heightof the cathode case.
 13. The flat non-aqueous electrolyte secondary cellaccording to claim 1, wherein the opening of the insulating gasket issealed through caulking by compressing said cathode case in thedirections of diameter and height, and one or two grooves are formed inthe lengthwise direction of an opening-sealed portion R in the cathodecase, to constitute a thin-plate portion.
 14. The flat non-aqueouselectrolyte secondary cell according to claim 1, wherein the thicknessof the thin-plate portion by groove processing is in the range of 0.07mm to 0.15 mm.
 15. The flat non-aqueous electrolyte secondary cellaccording to claim 1, wherein the anode case has at least one or moreshattering grooves having a concave shape in section.
 16. The flatnon-aqueous electrolyte secondary cell according to claim 1, wherein theshattering grooves having a concave shape in section are formed on theexternal surface of the anode case.
 17. The flat non-aqueous electrolytesecondary cell according to claim 1, wherein unevenness or protrusion isprovided in the inside of the cathode case and/or the anode case.
 18. Aflat non-aqueous electrolyte secondary cell comprising a metallic anodecase also serving as an anode terminal and a metallic cathode case alsoserving as a cathode terminal fit to each other via an insulatinggasket, the anode or cathode case having an opening-sealed structurecaulked by caulking and having in the inside thereof anelectricity-generating element including at least a cathode, a separatorand an anode and a non-aqueous electrolyte, wherein an electrode unit ina sheet form consisting of the cathode and the anode opposite to eachother via the separator is wound to form an electrode group, and thetotal sum of the areas of the opposing cathode and anode in thiselectrode group is larger than the area of the opening of saidinsulating gasket.
 19. The flat non-aqueous electrolyte secondary cellaccording to claim 18, wherein the electrode group comprising asheet-shaped electrode unit wound therein has been pressurized such thatthe cathode- and anode-opposing face is in a parallel direction to theflat plane of the flat cell, and there is no space in the wound core.20. The flat non-aqueous electrolyte secondary cell according to claim18, wherein the cathode and the anode, both in a sheet form, start fromapart positions to be wound via a separator, and the cathode and anodeare bent and wound such that the cathode- and anode-opposing face is ina parallel direction to the flat plane of the flat cell, thus forming anelectrode group.
 21. The flat non-aqueous electrolyte secondary cellaccording to claim 18, wherein the cathode comprises a cathode platehaving a cathode active material layer formed on one or both sides of acathode current-collecting body, the anode comprises an anode platehaving an anode active material layer formed on one or both sides of ananode current-collecting body, and the thickness of the active materiallayer coated on one side of each of the cathode and anodecurrent-collecting bodies is 0.03 mm to 0.40 mm.
 22. The flatnon-aqueous electrolyte secondary cell according to claim 18, whereinthe cathode comprises a cathode plate having a cathode active materiallayer formed on both sides of a cathode current-collecting body, theanode comprises an anode plate having an anode active material layerformed on both sides of an anode current-collecting body, each terminalthereof has each active substance layer formed on only one side, andeach exposed cathode current-collecting body is brought into contactwith the cathode case while each exposed anode current-collecting bodyis brought into contact with the anode case.
 23. The flat non-aqueouselectrolyte secondary cell according to claim 18, wherein a carbonmaterial having a developed graphite structure wherein the distance offace d₀₀₂ is 0.338 nm or less is used as the anode, and a solutioncomprising lithium borofluoride as a supporting electrolyte dissolved inethylene carbonate and γ-butyrolactone as major solvent is used as thenon-aqueous electrolyte.
 24. The flat non-aqueous electrolyte secondarycell according to claim 18, wherein the ratio by volume of ethylenecarbonate to γ-butyrolactone is from 0.3 to 1.0.
 25. The flatnon-aqueous electrolyte secondary cell according to claim 18, whereinthe concentration of the supporting electrolyte in the non-aqueouselectrolyte is 1.3 to 1.8 mol/l.
 26. The flat non-aqueous electrolytesecondary cell according to claim 18, wherein stainless steel preparedby adding 0.1 to 0.3% niobium, 0.1 to 0.3% titanium and 0.05 to 0.15%aluminum to ferrite-based stainless steel containing 28.50 to 32.00%chromium and 1.50 to 2.50% molybdenum is used as the cathode case alsoserving as a cathode terminal, or as a constituent member for a metallicpart brought directly into contact with the cathode active material. 27.The flat non-aqueous electrolyte secondary cell according to claim 18,wherein stainless steel prepared by adding 0.8 to 0.9% niobium, 0.05 to0.15% titanium and 0.20 to 0.30% copper to ferrite-based stainless steelcontaining 20.00 to 23.00% chromium and 1.50 to 2.50% molybdenum is usedas the cathode case also serving as a cathode terminal, or as aconstituent member for a metallic part brought directly into contactwith the cathode active material.
 28. The flat non-aqueous electrolytesecondary cell according to claim 18, wherein a metal net is providedbetween the cathode case and/or the anode case and the electrode group.29. The flat non-aqueous electrolyte secondary cell according to claim18, wherein a non-metal thermal insulator is provided between thecathode case and/or the anode case and the separator.
 30. The flatnon-aqueous electrolyte secondary cell according to claim 18, whereinthe opening of the insulating gasket is sealed through caulking bycompressing said cathode case in the directions of diameter and height,a cutting is provided in the side of the cathode case, and the width ofthe cutting is 0.1 π to 0.9 πrad in terms of central angle to thecircumference of the cathode case, and the depth of the cutting is 5 to30% of the height of the cathode case.
 31. The flat non-aqueouselectrolyte secondary cell according to claim 18, wherein the opening ofthe insulating gasket is sealed through caulking by compressing saidcathode case in the directions of diameter and height, and one or twogrooves are formed in the lengthwise direction of an opening-sealedportion R in the cathode case, to constitute a thin-plate portion. 32.The flat non-aqueous electrolyte secondary cell according to claim 18,wherein the thickness of the thin-plate portion by groove processing isin the range of 0.07 mm to 0.15 mm.
 33. The flat non-aqueous electrolytesecondary cell according to claim 18, wherein the anode case has atleast one or more shattering grooves having a concave shape in section.34. The flat non-aqueous electrolyte secondary cell according to claim18, wherein the shattering grooves having a concave shape in section areformed on the external surface of the anode case.
 35. The flatnon-aqueous electrolyte secondary cell according to claim 18, whereinunevenness or protrusion is provided in the inside of the cathode caseand/or the anode case.
 36. A flat non-aqueous electrolyte secondary cellcomprising a metallic anode case also serving as an anode terminal and ametallic cathode case also serving as a cathode terminal fit to eachother via an insulating gasket, the anode or cathode case having anopening-sealed structure caulked by caulking and having in the insidethereof an electricity-generating element including at least a cathode,a separator and an anode and a non-aqueous electrolyte, wherein asheet-shape cathode is wrapped with a separator except for in a partcontacting at inner face of cathode case, a sheet-shape anode is settledon the above sheet-shape cathode at right angles each other, and theyare bent alternately to form an electrode group, and the total sum ofthe areas of the opposing cathode and anode in this electrode group islarger than the area of the opening of said insulating gasket.
 37. Theflat non-aqueous electrolyte secondary cell according to claim 36,wherein the cathode and the anode, both in a sheet form, are arrangedvia a separator such that the cathode and the anode are crossed, thelower electrode is bent over the upper electrode via the separator, andthe other electrode is bent over said electrode, and thereafter thisprocedure is repeatedly carried out to form an electrode group.
 38. Theflat non-aqueous electrolyte secondary cell according to claim 36,wherein the cathode comprises a cathode plate having a cathode activematerial layer formed on both sides of a cathode current-collectingbody, the anode comprises an anode plate having an anode active materiallayer formed on both sides of an anode current-collecting body, eachterminal thereof has each active substance layer formed on only oneside, and each exposed cathode current-collecting body is brought intocontact with the cathode case while each exposed anodecurrent-collecting body is brought into contact with the anode case. 39.The flat non-aqueous electrolyte secondary cell according to claim 36,wherein the cathode comprises a cathode plate having a cathode activematerial layer formed on one or both sides of a cathodecurrent-collecting body, the anode comprises an anode plate having ananode active material layer formed on one or both sides of an anodecurrent-collecting body, one terminal of each of the cathode and anodeplates forms an electrically connecting part by exposing eachcurrent-collecting body, the electrically connecting portions of aplurality of cathode plates are exposed through the separator at thesame side so as to be electrically connected to the cathode case, whilethe electrically connecting portions of a plurality of anode plates areexposed through the separator at the other side to said cathode plates,so as to be electrically connected to the anode case.
 40. The flatnon-aqueous electrolyte secondary cell according to claim 36, wherein acarbon material having a developed graphite structure wherein thedistance of face d₀₀₂ is 0.338 nm or less is used as the anode, and asolution comprising lithium borofluoride as a supporting electrolytedissolved in ethylene carbonate and γ-butyrolactone as major solvent isused as the non-aqueous electrolyte
 41. The flat non-aqueous electrolytesecondary cell according to claim 36, wherein the ratio by volume ofethylene carbonate to γ-butyrolactone is from 0.3 to 1.0.
 42. The flatnon-aqueous electrolyte secondary cell according to claim 36, whereinthe concentration of the supporting electrolyte in the non-aqueouselectrolyte is 1.3 to 1.8 mol/l.
 43. The flat non-aqueous electrolytesecondary cell according to claim 36, wherein stainless steel preparedby adding 0.1 to 0.3% niobium, 0.1 to 0.3% titanium and 0.05 to 0.15%aluminum to ferrite-based stainless steel containing 28.50 to 32.00%chromium and 1.50 to 2.50% molybdenum is used as the cathode case alsoserving as a cathode terminal, or as a constituent member for a metallicpart brought directly into contact with the cathode active material. 44.The flat non-aqueous electrolyte secondary cell according to claim 36,wherein stainless steel prepared by adding 0.8 to 0.9% niobium, 0.05 to0.15% titanium and 0.20 to 0.30% copper to ferrite-based stainless steelcontaining 20.00 to 23.00% chromium and 1.50 to 2.50% molybdenum is usedas the cathode case also serving as a cathode terminal, or as aconstituent member for a metallic part brought directly into contactwith the cathode active material.
 45. The flat non-aqueous electrolytesecondary cell according to claim 36, wherein a metal net is providedbetween the cathode case and/or the anode case and the electrode group.46. The flat non-aqueous electrolyte secondary cell according to claim36, wherein a non-metal thermal insulator is provided between thecathode case and/or the anode case and the separator.
 47. The flatnon-aqueous electrolyte secondary cell according to claim 36, whereinthe opening of the insulating gasket is sealed through caulking bycompressing said cathode case in the directions of diameter and height,a cutting is provided in the side of the cathode case, and the width ofthe cutting is 0.1 π to 0.9 πrad in terms of central angle to thecircumference of the cathode case, and the depth of the cutting is 5 to30% of the height of the cathode case.
 48. The flat non-aqueouselectrolyte secondary cell according to claim 36, wherein the opening ofthe insulating gasket is sealed through caulking by compressing saidcathode case in the directions of diameter and height, and one or twogrooves are formed in the lengthwise direction of an opening-sealedportion R in the cathode case, to constitute a thin-plate portion. 49.The flat non-aqueous electrolyte secondary cell according to claim 36,wherein the thickness of the thin-plate portion by groove processing isin the range of 0.07 mm to 0.15 mm.
 50. The flat non-aqueous electrolytesecondary cell according to claim 36, wherein the anode case has atleast one or more shattering grooves having a concave shape in section.51. The flat non-aqueous electrolyte secondary cell according to claim36, wherein the shattering grooves having a concave shape in section areformed on the external surface of the anode case.
 52. The flatnon-aqueous electrolyte secondary cell according to claim 36, whereinunevenness or protrusion is provided in the inside of the cathode caseand/or the anode case.
 53. A flat non-aqueous electrolyte secondary cellcomprising a metallic cell case also serving as an electrode terminal,an opening-sealing plate for sealing an opening in said cell case, andanother electrode terminal arranged via an insulator in an openingprovided in a part of the opening-sealing plate, said cell case beingprovided inside with an electricity-generating element including atleast a cathode, a separator and an anode and a non-aqueous electrolyte,wherein an electrode group consisting of an electrode unit having thecathode and the anode opposite to each other via the separator isformed, and the total sum of the areas of the opposing cathode and anodein this electrode group is larger than the area of the opening of saidopening-sealing plate.
 54. The flat non-aqueous electrolyte secondarycell according to claim 53, wherein a plurality of the electrode unitsare laminated and the cathodes are mutually electrically connected andthe anodes are mutually electrically connected, to form an electrodegroup respectively.
 55. The flat non-aqueous electrolyte secondary cellaccording to claim 53, wherein an electrode group comprising thesheet-shaped cathode and anode wound via a separator is accommodated inthe cell. 56 The flat non-aqueous electrolyte secondary cell accordingto claim 53, wherein a current-collecting plate integrated electricallyin the terminal of the other electrode is arranged, and saidcurrent-collecting plate is electrically connected to the cathode oranode.
 57. The flat non-aqueous electrolyte secondary cell according toclaim 53, wherein the cathode comprises a cathode plate having a cathodeactive material layer formed on one or both sides of a cathodecurrent-collecting body, the anode comprises an anode plate having ananode active material layer formed on one or both sides of an anodecurrent-collecting body, and the thickness of the active material layercoated on one side of each of the cathode and anode current-collectingbodies is 0.03 mm to 0.40 mm.
 58. The flat non-aqueous electrolytesecondary cell according to claim 53, wherein the cathode comprises acathode plate having a cathode active material layer formed on one orboth sides of a cathode current-collecting body, the anode comprises ananode plate having an anode active material layer formed on one or bothsides of an anode current-collecting body, one terminal of each of thecathode and anode plates forms an electrically connecting part byexposing each current-collecting body, the electrically connectingportions of a plurality of cathode plates are exposed through theseparator at the same side so as to be electrically connected to thecathode case, while the electrically connecting portions of a pluralityof anode plates are exposed through the separator at the other side tosaid cathode plates, so as to be electrically connected to the anodecase.
 59. The flat non-aqueous electrolyte secondary cell according toclaim 53, wherein a carbon material having a developed graphitestructure wherein the distance of face d₀₀₂ is 0.338 nm or less is usedas the anode, and a solution comprising lithium borofluoride as asupporting electrolyte dissolved in ethylene carbonate andγ-butyrolactone as major solvent is used as the non-aqueous electrolyte.60. The flat non-aqueous electrolyte secondary cell according to claim53, wherein the ratio by volume of ethylene carbonate to γ-butyrolactoneis from 0.3 to 1.0.
 61. The flat non-aqueous electrolyte secondary cellaccording to claim 53, wherein the concentration of the supportingelectrolyte in the non-aqueous electrolyte is 1.3 to 1.8 mol/l.
 62. Theflat non-aqueous electrolyte secondary cell according to claim 53,wherein stainless steel prepared by adding 0.1 to 0.3% niobium, 0.1 to0.3% titanium and 0.05 to 0.15% aluminum to ferrite-based stainlesssteel containing 28.50 to 32.00% chromium and 1.50 to 2.50% molybdenumis used as the cathode case also serving as a cathode terminal, or as aconstituent member for a metallic part brought directly into contactwith the cathode active material.
 63. The flat non-aqueous electrolytesecondary cell according to claim 53, wherein stainless steel preparedby adding 0.8 to 0.9% niobium, 0.05 to 0.15% titanium and 0.20 to 0.30%copper to ferrite-based stainless steel containing 20.00 to 23.00%chromium and 1.50 to 2.50% molybdenum is used as the cathode case alsoserving as a cathode terminal, or as a constituent member for a metallicpart brought directly into contact with the cathode active material. 64.The flat non-aqueous electrolyte secondary cell according to claim 53,wherein a metal net is provided between the cathode case and/or theanode case and the electrode group.
 65. The flat non-aqueous electrolytesecondary cell according to claim 53, wherein a non-metal thermalinsulator is provided between the cathode case and/or the anode case andthe separator.
 66. The flat non-aqueous electrolyte secondary cellaccording to claim 53, wherein the anode case has at least one or moreshattering grooves having a concave shape in section.
 67. The flatnon-aqueous electrolyte secondary cell according to claim 53, whereinthe shattering grooves having a concave shape in section are formed onthe external surface of the anode case.
 68. The flat non-aqueouselectrolyte secondary cell according to claim 53, wherein unevenness orprotrusion is provided in the inside of the cathode case and/or theanode case.